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 $216.48   13.651%   $246.0317   $246.03   $246.05   $246.00  
  Purchase #2 $88.78   9.372%   $97.1005   $97.10   $97.10   $97.10  
  Purchase #3 $145.40   5.478%   $153.365   $153.37   $153.35   $153.40  
  Purchase #4 $237.72   8.348%   $257.5649   $257.56   $257.55   $257.60  
  Purchase #5 $101.55   12.439%   $114.1818   $114.18   $114.20   $114.20  
  Purchase #6 $201.93   6.344%   $214.7404   $214.74   $214.75   $214.70  
  Purchase #7 $48.51   7.871%   $52.3282   $52.33   $52.35   $52.30  
  7 purchase totals = $1,040.37       $1,135.3125   $1,135.31   $1,135.35   $1,135.30