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 $109.31   8.355%   $118.4429   $118.44   $118.45   $118.40  
  Purchase #2 $153.60   4.212%   $160.0696   $160.07   $160.05   $160.10  
  Purchase #3 $38.48   6.119%   $40.8346   $40.83   $40.85   $40.80  
  Purchase #4 $74.40   5.791%   $78.7085   $78.71   $78.70   $78.70  
  Purchase #5 $236.56   9.107%   $258.1035   $258.10   $258.10   $258.10  
  Purchase #6 $82.61   7.419%   $88.7388   $88.74   $88.75   $88.70  
  Purchase #7 $203.25   12.830%   $229.327   $229.33   $229.35   $229.30  
  7 purchase totals = $898.21       $974.2249   $974.22   $974.25   $974.10