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 $10.48   6.501%   $11.1613   $11.16   $11.15   $11.20  
  Purchase #2 $175.47   13.516%   $199.1865   $199.19   $199.20   $199.20  
  Purchase #3 $167.69   12.464%   $188.5909   $188.59   $188.60   $188.60  
  Purchase #4 $83.64   9.236%   $91.365   $91.37   $91.35   $91.40  
  Purchase #5 $138.33   3.342%   $142.953   $142.95   $142.95   $143.00  
  Purchase #6 $175.48   13.580%   $199.3102   $199.31   $199.30   $199.30  
  Purchase #7 $60.96   6.221%   $64.7523   $64.75   $64.75   $64.80  
  7 purchase totals = $812.05       $897.3192   $897.32   $897.30   $897.50