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 $228.49   11.255%   $254.2065   $254.21   $254.20   $254.20  
  Purchase #2 $23.43   7.499%   $25.187   $25.19   $25.20   $25.20  
  Purchase #3 $244.77   11.275%   $272.3678   $272.37   $272.35   $272.40  
  Purchase #4 $187.93   9.412%   $205.618   $205.62   $205.60   $205.60  
  Purchase #5 $118.38   10.424%   $130.7199   $130.72   $130.70   $130.70  
  Purchase #6 $54.29   3.495%   $56.1874   $56.19   $56.20   $56.20  
  Purchase #7 $121.66   12.385%   $136.7276   $136.73   $136.75   $136.70  
  7 purchase totals = $978.95       $1,081.0142   $1,081.03   $1,081.00   $1,081.00