Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $162.86   7.226%   $174.6283   $174.63   $174.65   $174.60  
  Purchase #2 $160.98   6.210%   $170.9769   $170.98   $171.00   $171.00  
  Purchase #3 $103.32   12.273%   $116.0005   $116.00   $116.00   $116.00  
  Purchase #4 $191.54   10.364%   $211.3912   $211.39   $211.40   $211.40  
  Purchase #5 $246.33   4.531%   $257.4912   $257.49   $257.50   $257.50  
  Purchase #6 $184.97   8.728%   $201.1142   $201.11   $201.10   $201.10  
  Purchase #7 $101.94   7.759%   $109.8495   $109.85   $109.85   $109.80  
  7 purchase totals = $1,151.94       $1,241.4518   $1,241.45   $1,241.50   $1,241.40