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 $116.61   12.374%   $131.0393   $131.04   $131.05   $131.00  
  Purchase #2 $153.69   13.824%   $174.9361   $174.94   $174.95   $174.90  
  Purchase #3 $76.89   5.724%   $81.2912   $81.29   $81.30   $81.30  
  Purchase #4 $45.40   9.575%   $49.7471   $49.75   $49.75   $49.70  
  Purchase #5 $164.79   3.285%   $170.2034   $170.20   $170.20   $170.20  
  Purchase #6 $160.59   4.201%   $167.3364   $167.34   $167.35   $167.30  
  Purchase #7 $155.44   3.364%   $160.669   $160.67   $160.65   $160.70  
  7 purchase totals = $873.41       $935.2225   $935.23   $935.25   $935.10