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 $207.37   11.213%   $230.6224   $230.62   $230.60   $230.60  
  Purchase #2 $149.49   10.746%   $165.5542   $165.55   $165.55   $165.60  
  Purchase #3 $23.38   6.802%   $24.9703   $24.97   $24.95   $25.00  
  Purchase #4 $55.69   6.148%   $59.1138   $59.11   $59.10   $59.10  
  Purchase #5 $65.60   4.843%   $68.777   $68.78   $68.80   $68.80  
  Purchase #6 $189.90   11.813%   $212.3329   $212.33   $212.35   $212.30  
  Purchase #7 $148.46   5.234%   $156.2304   $156.23   $156.25   $156.20  
  7 purchase totals = $839.89       $917.6010   $917.59   $917.60   $917.60