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 $225.93   9.518%   $247.434   $247.43   $247.45   $247.40  
  Purchase #2 $245.54   3.549%   $254.2542   $254.25   $254.25   $254.30  
  Purchase #3 $49.37   13.839%   $56.2023   $56.20   $56.20   $56.20  
  Purchase #4 $67.55   6.378%   $71.8583   $71.86   $71.85   $71.90  
  Purchase #5 $148.96   11.177%   $165.6093   $165.61   $165.60   $165.60  
  Purchase #6 $186.39   13.476%   $211.5079   $211.51   $211.50   $211.50  
  Purchase #7 $210.95   13.794%   $240.0484   $240.05   $240.05   $240.00  
  7 purchase totals = $1,134.69       $1,246.9144   $1,246.91   $1,246.90   $1,246.90