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 $54.67   11.782%   $61.1112   $61.11   $61.10   $61.10  
  Purchase #2 $226.98   4.738%   $237.7343   $237.73   $237.75   $237.70  
  Purchase #3 $243.92   6.260%   $259.1894   $259.19   $259.20   $259.20  
  Purchase #4 $160.98   10.296%   $177.5545   $177.55   $177.55   $177.60  
  Purchase #5 $197.89   11.338%   $220.3268   $220.33   $220.35   $220.30  
  Purchase #6 $135.60   3.310%   $140.0884   $140.09   $140.10   $140.10  
  Purchase #7 $128.38   12.371%   $144.2619   $144.26   $144.25   $144.30  
  7 purchase totals = $1,148.42       $1,240.2665   $1,240.26   $1,240.30   $1,240.30