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 $62.33   11.366%   $69.4144   $69.41   $69.40   $69.40  
  Purchase #2 $95.25   10.785%   $105.5227   $105.52   $105.50   $105.50  
  Purchase #3 $111.52   12.768%   $125.7589   $125.76   $125.75   $125.80  
  Purchase #4 $235.77   11.592%   $263.1005   $263.10   $263.10   $263.10  
  Purchase #5 $109.56   8.459%   $118.8277   $118.83   $118.85   $118.80  
  Purchase #6 $206.86   12.456%   $232.6265   $232.63   $232.65   $232.60  
  Purchase #7 $217.72   13.696%   $247.5389   $247.54   $247.55   $247.50  
  7 purchase totals = $1,039.01       $1,162.7896   $1,162.79   $1,162.80   $1,162.70