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 $238.63   7.514%   $256.5607   $256.56   $256.55   $256.60  
  Purchase #2 $145.30   10.225%   $160.1569   $160.16   $160.15   $160.20  
  Purchase #3 $83.41   12.218%   $93.601   $93.60   $93.60   $93.60  
  Purchase #4 $163.89   10.145%   $180.5166   $180.52   $180.50   $180.50  
  Purchase #5 $55.62   5.497%   $58.6774   $58.68   $58.70   $58.70  
  Purchase #6 $166.99   5.268%   $175.787   $175.79   $175.80   $175.80  
  Purchase #7 $25.39   4.779%   $26.6034   $26.60   $26.60   $26.60  
  7 purchase totals = $879.23       $951.9030   $951.91   $951.90   $952.00