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 $64.28   5.838%   $68.0327   $68.03   $68.05   $68.00  
  Purchase #2 $144.39   8.142%   $156.1462   $156.15   $156.15   $156.10  
  Purchase #3 $168.63   11.529%   $188.0714   $188.07   $188.05   $188.10  
  Purchase #4 $178.57   13.165%   $202.0787   $202.08   $202.10   $202.10  
  Purchase #5 $31.61   7.465%   $33.9697   $33.97   $33.95   $34.00  
  Purchase #6 $167.92   5.845%   $177.7349   $177.73   $177.75   $177.70  
  Purchase #7 $119.46   6.134%   $126.7877   $126.79   $126.80   $126.80  
  7 purchase totals = $874.86       $952.8213   $952.82   $952.85   $952.80