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 $184.98   10.697%   $204.7673   $204.77   $204.75   $204.80  
  Purchase #2 $136.55   6.375%   $145.2551   $145.26   $145.25   $145.30  
  Purchase #3 $29.63   7.849%   $31.9557   $31.96   $31.95   $32.00  
  Purchase #4 $217.72   4.231%   $226.9317   $226.93   $226.95   $226.90  
  Purchase #5 $155.25   12.481%   $174.6268   $174.63   $174.65   $174.60  
  Purchase #6 $248.73   8.830%   $270.6929   $270.69   $270.70   $270.70  
  Purchase #7 $100.32   5.145%   $105.4815   $105.48   $105.50   $105.50  
  7 purchase totals = $1,073.18       $1,159.7110   $1,159.72   $1,159.75   $1,159.80