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 $30.59   9.305%   $33.4364   $33.44   $33.45   $33.40  
  Purchase #2 $181.93   6.714%   $194.1448   $194.14   $194.15   $194.10  
  Purchase #3 $60.77   8.182%   $65.7422   $65.74   $65.75   $65.70  
  Purchase #4 $46.54   5.193%   $48.9568   $48.96   $48.95   $49.00  
  Purchase #5 $92.94   6.333%   $98.8259   $98.83   $98.85   $98.80  
  Purchase #6 $120.30   9.626%   $131.8801   $131.88   $131.90   $131.90  
  Purchase #7 $192.33   8.821%   $209.2954   $209.30   $209.30   $209.30  
  7 purchase totals = $725.40       $782.2816   $782.29   $782.35   $782.20