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 $156.55   6.651%   $166.9621   $166.96   $166.95   $167.00  
  Purchase #2 $33.46   13.425%   $37.952   $37.95   $37.95   $38.00  
  Purchase #3 $134.40   11.283%   $149.5644   $149.56   $149.55   $149.60  
  Purchase #4 $190.46   9.204%   $207.9899   $207.99   $208.00   $208.00  
  Purchase #5 $91.92   11.669%   $102.6461   $102.65   $102.65   $102.60  
  Purchase #6 $38.93   10.478%   $43.0091   $43.01   $43.00   $43.00  
  Purchase #7 $234.40   5.747%   $247.871   $247.87   $247.85   $247.90  
  7 purchase totals = $880.12       $955.9946   $955.99   $955.95   $956.10