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 $97.37   7.718%   $104.885   $104.89   $104.90   $104.90  
  Purchase #2 $76.83   7.581%   $82.6545   $82.65   $82.65   $82.70  
  Purchase #3 $174.86   8.514%   $189.7476   $189.75   $189.75   $189.70  
  Purchase #4 $148.43   6.308%   $157.793   $157.79   $157.80   $157.80  
  Purchase #5 $98.83   7.397%   $106.1405   $106.14   $106.15   $106.10  
  Purchase #6 $216.71   3.731%   $224.7955   $224.80   $224.80   $224.80  
  Purchase #7 $166.85   13.768%   $189.8219   $189.82   $189.80   $189.80  
  7 purchase totals = $979.88       $1,055.8380   $1,055.84   $1,055.85   $1,055.80