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 $141.93   7.781%   $152.9736   $152.97   $152.95   $153.00  
  Purchase #2 $24.41   3.358%   $25.2297   $25.23   $25.25   $25.20  
  Purchase #3 $150.54   5.815%   $159.2939   $159.29   $159.30   $159.30  
  Purchase #4 $86.46   9.133%   $94.3564   $94.36   $94.35   $94.40  
  Purchase #5 $117.33   4.238%   $122.3024   $122.30   $122.30   $122.30  
  Purchase #6 $214.86   6.658%   $229.1654   $229.17   $229.15   $229.20  
  Purchase #7 $118.35   3.514%   $122.5088   $122.51   $122.50   $122.50  
  7 purchase totals = $853.88       $905.8302   $905.83   $905.80   $905.90