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 $48.67   11.342%   $54.1902   $54.19   $54.20   $54.20  
  Purchase #2 $194.67   9.789%   $213.7262   $213.73   $213.75   $213.70  
  Purchase #3 $55.29   6.283%   $58.7639   $58.76   $58.75   $58.80  
  Purchase #4 $153.51   7.642%   $165.2412   $165.24   $165.25   $165.20  
  Purchase #5 $216.29   12.107%   $242.4762   $242.48   $242.50   $242.50  
  Purchase #6 $99.86   8.806%   $108.6537   $108.65   $108.65   $108.70  
  Purchase #7 $93.36   7.404%   $100.2724   $100.27   $100.25   $100.30  
  7 purchase totals = $861.65       $943.3238   $943.32   $943.35   $943.40