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 $84.65   7.873%   $91.3145   $91.31   $91.30   $91.30  
  Purchase #2 $142.95   13.108%   $161.6879   $161.69   $161.70   $161.70  
  Purchase #3 $224.71   5.457%   $236.9724   $236.97   $236.95   $237.00  
  Purchase #4 $101.99   4.263%   $106.3378   $106.34   $106.35   $106.30  
  Purchase #5 $149.43   4.300%   $155.8555   $155.86   $155.85   $155.90  
  Purchase #6 $105.98   8.208%   $114.6788   $114.68   $114.70   $114.70  
  Purchase #7 $151.57   5.582%   $160.0306   $160.03   $160.05   $160.00  
  7 purchase totals = $961.28       $1,026.8775   $1,026.88   $1,026.90   $1,026.90