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 $62.42   7.172%   $66.8968   $66.90   $66.90   $66.90  
  Purchase #2 $212.81   9.347%   $232.7014   $232.70   $232.70   $232.70  
  Purchase #3 $69.90   11.500%   $77.9385   $77.94   $77.95   $77.90  
  Purchase #4 $29.31   6.560%   $31.2327   $31.23   $31.25   $31.20  
  Purchase #5 $155.97   9.732%   $171.149   $171.15   $171.15   $171.10  
  Purchase #6 $22.35   10.495%   $24.6956   $24.70   $24.70   $24.70  
  Purchase #7 $229.62   5.503%   $242.256   $242.26   $242.25   $242.30  
  7 purchase totals = $782.38       $846.8700   $846.88   $846.90   $846.80