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 $244.50   3.320%   $252.6174   $252.62   $252.60   $252.60  
  Purchase #2 $99.95   4.408%   $104.3558   $104.36   $104.35   $104.40  
  Purchase #3 $171.95   8.721%   $186.9458   $186.95   $186.95   $186.90  
  Purchase #4 $51.38   12.744%   $57.9279   $57.93   $57.95   $57.90  
  Purchase #5 $142.82   11.419%   $159.1286   $159.13   $159.15   $159.10  
  Purchase #6 $169.48   11.744%   $189.3837   $189.38   $189.40   $189.40  
  Purchase #7 $54.65   11.486%   $60.9271   $60.93   $60.95   $60.90  
  7 purchase totals = $934.73       $1,011.2863   $1,011.30   $1,011.35   $1,011.20