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 $155.54   13.257%   $176.1599   $176.16   $176.15   $176.20  
  Purchase #2 $247.84   6.865%   $264.8542   $264.85   $264.85   $264.90  
  Purchase #3 $59.44   4.530%   $62.1326   $62.13   $62.15   $62.10  
  Purchase #4 $233.84   8.227%   $253.078   $253.08   $253.10   $253.10  
  Purchase #5 $195.38   4.294%   $203.7696   $203.77   $203.75   $203.80  
  Purchase #6 $51.82   6.736%   $55.3106   $55.31   $55.30   $55.30  
  Purchase #7 $176.80   9.803%   $194.1317   $194.13   $194.15   $194.10  
  7 purchase totals = $1,120.66       $1,209.4366   $1,209.43   $1,209.45   $1,209.50