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 $146.60   5.698%   $154.9533   $154.95   $154.95   $155.00  
  Purchase #2 $68.29   11.253%   $75.9747   $75.97   $75.95   $76.00  
  Purchase #3 $202.82   4.760%   $212.4742   $212.47   $212.45   $212.50  
  Purchase #4 $229.31   13.200%   $259.5789   $259.58   $259.60   $259.60  
  Purchase #5 $72.82   10.766%   $80.6598   $80.66   $80.65   $80.70  
  Purchase #6 $236.57   7.172%   $253.5368   $253.54   $253.55   $253.50  
  Purchase #7 $236.73   11.157%   $263.142   $263.14   $263.15   $263.10  
  7 purchase totals = $1,193.14       $1,300.3197   $1,300.31   $1,300.30   $1,300.40