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 $235.38   11.756%   $263.0513   $263.05   $263.05   $263.10  
  Purchase #2 $219.54   10.200%   $241.9331   $241.93   $241.95   $241.90  
  Purchase #3 $167.68   9.305%   $183.2826   $183.28   $183.30   $183.30  
  Purchase #4 $40.51   11.829%   $45.3019   $45.30   $45.30   $45.30  
  Purchase #5 $233.90   11.386%   $260.5319   $260.53   $260.55   $260.50  
  Purchase #6 $103.49   9.846%   $113.6796   $113.68   $113.70   $113.70  
  Purchase #7 $140.37   11.194%   $156.083   $156.08   $156.10   $156.10  
  7 purchase totals = $1,140.87       $1,263.8634   $1,263.85   $1,263.95   $1,263.90