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 $233.48   8.699%   $253.7904   $253.79   $253.80   $253.80  
  Purchase #2 $177.77   12.153%   $199.3744   $199.37   $199.35   $199.40  
  Purchase #3 $142.95   11.655%   $159.6108   $159.61   $159.60   $159.60  
  Purchase #4 $43.25   5.170%   $45.486   $45.49   $45.50   $45.50  
  Purchase #5 $69.67   12.224%   $78.1865   $78.19   $78.20   $78.20  
  Purchase #6 $60.52   4.203%   $63.0637   $63.06   $63.05   $63.10  
  Purchase #7 $222.37   9.712%   $243.9666   $243.97   $243.95   $244.00  
  7 purchase totals = $950.01       $1,043.4784   $1,043.48   $1,043.45   $1,043.60