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 $49.48   10.838%   $54.8426   $54.84   $54.85   $54.80  
  Purchase #2 $108.96   12.142%   $122.1899   $122.19   $122.20   $122.20  
  Purchase #3 $218.84   4.276%   $228.1976   $228.20   $228.20   $228.20  
  Purchase #4 $148.43   9.232%   $162.1331   $162.13   $162.15   $162.10  
  Purchase #5 $184.44   8.750%   $200.5785   $200.58   $200.60   $200.60  
  Purchase #6 $249.93   10.242%   $275.5278   $275.53   $275.55   $275.50  
  Purchase #7 $23.40   12.766%   $26.3872   $26.39   $26.40   $26.40  
  7 purchase totals = $983.48       $1,069.8567   $1,069.86   $1,069.95   $1,069.80