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 $245.87   3.551%   $254.6008   $254.60   $254.60   $254.60  
  Purchase #2 $57.74   8.825%   $62.8356   $62.84   $62.85   $62.80  
  Purchase #3 $102.67   10.404%   $113.3518   $113.35   $113.35   $113.40  
  Purchase #4 $15.81   4.759%   $16.5624   $16.56   $16.55   $16.60  
  Purchase #5 $231.98   6.781%   $247.7106   $247.71   $247.70   $247.70  
  Purchase #6 $110.48   3.456%   $114.2982   $114.30   $114.30   $114.30  
  Purchase #7 $55.51   5.313%   $58.4592   $58.46   $58.45   $58.50  
  7 purchase totals = $820.06       $867.8186   $867.82   $867.80   $867.90