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 $167.62   11.562%   $187.0002   $187.00   $187.00   $187.00  
  Purchase #2 $226.37   8.811%   $246.3155   $246.32   $246.30   $246.30  
  Purchase #3 $103.99   3.491%   $107.6203   $107.62   $107.60   $107.60  
  Purchase #4 $138.26   13.196%   $156.5048   $156.50   $156.50   $156.50  
  Purchase #5 $197.52   4.278%   $205.9699   $205.97   $205.95   $206.00  
  Purchase #6 $211.48   6.428%   $225.0739   $225.07   $225.05   $225.10  
  Purchase #7 $137.68   7.685%   $148.2607   $148.26   $148.25   $148.30  
  7 purchase totals = $1,182.92       $1,276.7453   $1,276.74   $1,276.65   $1,276.80