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 $150.67   10.814%   $166.9635   $166.96   $166.95   $167.00  
  Purchase #2 $84.54   12.663%   $95.2453   $95.25   $95.25   $95.20  
  Purchase #3 $178.57   5.591%   $188.5538   $188.55   $188.55   $188.60  
  Purchase #4 $139.93   11.134%   $155.5098   $155.51   $155.50   $155.50  
  Purchase #5 $246.67   10.504%   $272.5802   $272.58   $272.60   $272.60  
  Purchase #6 $218.55   5.470%   $230.5047   $230.50   $230.50   $230.50  
  Purchase #7 $182.98   8.205%   $197.9935   $197.99   $198.00   $198.00  
  7 purchase totals = $1,201.91       $1,307.3508   $1,307.34   $1,307.35   $1,307.40