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 $21.25   8.592%   $23.0758   $23.08   $23.10   $23.10  
  Purchase #2 $123.60   4.500%   $129.162   $129.16   $129.15   $129.20  
  Purchase #3 $245.78   6.669%   $262.1711   $262.17   $262.15   $262.20  
  Purchase #4 $145.42   4.499%   $151.9624   $151.96   $151.95   $152.00  
  Purchase #5 $29.64   10.618%   $32.7872   $32.79   $32.80   $32.80  
  Purchase #6 $205.46   12.829%   $231.8185   $231.82   $231.80   $231.80  
  Purchase #7 $71.69   5.842%   $75.8781   $75.88   $75.90   $75.90  
  7 purchase totals = $842.84       $906.8551   $906.86   $906.85   $907.00