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 $230.56   12.241%   $258.7828   $258.78   $258.80   $258.80  
  Purchase #2 $93.95   11.351%   $104.6143   $104.61   $104.60   $104.60  
  Purchase #3 $206.82   12.586%   $232.8504   $232.85   $232.85   $232.90  
  Purchase #4 $187.88   4.592%   $196.5074   $196.51   $196.50   $196.50  
  Purchase #5 $173.80   9.592%   $190.4709   $190.47   $190.45   $190.50  
  Purchase #6 $219.50   7.336%   $235.6025   $235.60   $235.60   $235.60  
  Purchase #7 $23.47   12.181%   $26.3289   $26.33   $26.35   $26.30  
  7 purchase totals = $1,135.98       $1,245.1572   $1,245.15   $1,245.15   $1,245.20