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 $68.66   6.592%   $73.1861   $73.19   $73.20   $73.20  
  Purchase #2 $85.92   13.713%   $97.7022   $97.70   $97.70   $97.70  
  Purchase #3 $34.79   11.532%   $38.802   $38.80   $38.80   $38.80  
  Purchase #4 $83.52   6.655%   $89.0783   $89.08   $89.10   $89.10  
  Purchase #5 $209.53   6.494%   $223.1369   $223.14   $223.15   $223.10  
  Purchase #6 $228.88   13.206%   $259.1059   $259.11   $259.10   $259.10  
  Purchase #7 $43.39   9.483%   $47.5047   $47.50   $47.50   $47.50  
  7 purchase totals = $754.69       $828.5161   $828.52   $828.55   $828.50