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 $218.83   12.629%   $246.466   $246.47   $246.45   $246.50  
  Purchase #2 $128.25   4.349%   $133.8276   $133.83   $133.85   $133.80  
  Purchase #3 $109.38   13.633%   $124.2918   $124.29   $124.30   $124.30  
  Purchase #4 $186.59   3.625%   $193.3539   $193.35   $193.35   $193.40  
  Purchase #5 $14.58   6.608%   $15.5434   $15.54   $15.55   $15.50  
  Purchase #6 $83.87   3.129%   $86.4943   $86.49   $86.50   $86.50  
  Purchase #7 $238.73   7.279%   $256.1072   $256.11   $256.10   $256.10  
  7 purchase totals = $980.23       $1,056.0842   $1,056.08   $1,056.10   $1,056.10