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 $54.60   11.654%   $60.9631   $60.96   $60.95   $61.00  
  Purchase #2 $240.64   7.640%   $259.0249   $259.02   $259.00   $259.00  
  Purchase #3 $174.73   8.637%   $189.8214   $189.82   $189.80   $189.80  
  Purchase #4 $64.34   5.819%   $68.0839   $68.08   $68.10   $68.10  
  Purchase #5 $95.35   4.817%   $99.943   $99.94   $99.95   $99.90  
  Purchase #6 $16.50   4.827%   $17.2965   $17.30   $17.30   $17.30  
  Purchase #7 $210.60   11.574%   $234.9748   $234.97   $234.95   $235.00  
  7 purchase totals = $856.76       $930.1076   $930.09   $930.05   $930.10