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 $126.33   11.592%   $140.9742   $140.97   $140.95   $141.00  
  Purchase #2 $224.32   11.315%   $249.7018   $249.70   $249.70   $249.70  
  Purchase #3 $83.71   12.560%   $94.224   $94.22   $94.20   $94.20  
  Purchase #4 $58.73   11.683%   $65.5914   $65.59   $65.60   $65.60  
  Purchase #5 $248.50   10.355%   $274.2322   $274.23   $274.25   $274.20  
  Purchase #6 $189.49   12.203%   $212.6135   $212.61   $212.60   $212.60  
  Purchase #7 $181.52   6.756%   $193.7835   $193.78   $193.80   $193.80  
  7 purchase totals = $1,112.60       $1,231.1206   $1,231.10   $1,231.10   $1,231.10