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 $87.32   7.394%   $93.7764   $93.78   $93.80   $93.80  
  Purchase #2 $60.80   6.824%   $64.949   $64.95   $64.95   $64.90  
  Purchase #3 $59.34   7.817%   $63.9786   $63.98   $64.00   $64.00  
  Purchase #4 $17.30   12.521%   $19.4661   $19.47   $19.45   $19.50  
  Purchase #5 $248.70   13.532%   $282.3541   $282.35   $282.35   $282.40  
  Purchase #6 $187.33   12.543%   $210.8268   $210.83   $210.85   $210.80  
  Purchase #7 $59.94   5.263%   $63.0946   $63.09   $63.10   $63.10  
  7 purchase totals = $720.73       $798.4456   $798.45   $798.50   $798.50