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 $41.88   6.703%   $44.6872   $44.69   $44.70   $44.70  
  Purchase #2 $171.48   13.572%   $194.7533   $194.75   $194.75   $194.80  
  Purchase #3 $88.53   6.744%   $94.5005   $94.50   $94.50   $94.50  
  Purchase #4 $201.42   9.461%   $220.4763   $220.48   $220.50   $220.50  
  Purchase #5 $24.92   6.288%   $26.487   $26.49   $26.50   $26.50  
  Purchase #6 $187.49   8.600%   $203.6141   $203.61   $203.60   $203.60  
  Purchase #7 $43.98   11.339%   $48.9669   $48.97   $48.95   $49.00  
  7 purchase totals = $759.70       $833.4853   $833.49   $833.50   $833.60