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 $69.95   7.640%   $75.2942   $75.29   $75.30   $75.30  
  Purchase #2 $236.69   11.283%   $263.3957   $263.40   $263.40   $263.40  
  Purchase #3 $200.92   5.357%   $211.6833   $211.68   $211.70   $211.70  
  Purchase #4 $192.72   7.756%   $207.6674   $207.67   $207.65   $207.70  
  Purchase #5 $217.69   13.451%   $246.9715   $246.97   $246.95   $247.00  
  Purchase #6 $99.93   4.107%   $104.0341   $104.03   $104.05   $104.00  
  Purchase #7 $116.88   12.649%   $131.6642   $131.66   $131.65   $131.70  
  7 purchase totals = $1,134.78       $1,240.7104   $1,240.70   $1,240.70   $1,240.80