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 $109.98   12.293%   $123.4998   $123.50   $123.50   $123.50  
  Purchase #2 $62.41   9.823%   $68.5405   $68.54   $68.55   $68.50  
  Purchase #3 $73.56   9.547%   $80.5828   $80.58   $80.60   $80.60  
  Purchase #4 $194.73   4.612%   $203.7109   $203.71   $203.70   $203.70  
  Purchase #5 $222.67   8.528%   $241.6593   $241.66   $241.65   $241.70  
  Purchase #6 $90.30   5.778%   $95.5175   $95.52   $95.50   $95.50  
  Purchase #7 $234.60   12.609%   $264.1807   $264.18   $264.20   $264.20  
  7 purchase totals = $988.25       $1,077.6915   $1,077.69   $1,077.70   $1,077.70