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 $246.38   8.608%   $267.5884   $267.59   $267.60   $267.60  
  Purchase #2 $218.31   8.658%   $237.2113   $237.21   $237.20   $237.20  
  Purchase #3 $72.89   12.414%   $81.9386   $81.94   $81.95   $81.90  
  Purchase #4 $42.45   8.678%   $46.1338   $46.13   $46.15   $46.10  
  Purchase #5 $215.75   6.478%   $229.7263   $229.73   $229.75   $229.70  
  Purchase #6 $150.29   10.512%   $166.0885   $166.09   $166.10   $166.10  
  Purchase #7 $212.32   3.256%   $219.2331   $219.23   $219.25   $219.20  
  7 purchase totals = $1,158.39       $1,247.9200   $1,247.92   $1,248.00   $1,247.80