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 $62.39   6.620%   $66.5202   $66.52   $66.50   $66.50  
  Purchase #2 $41.42   10.187%   $45.6395   $45.64   $45.65   $45.60  
  Purchase #3 $124.49   7.429%   $133.7384   $133.74   $133.75   $133.70  
  Purchase #4 $244.33   8.634%   $265.4255   $265.43   $265.45   $265.40  
  Purchase #5 $86.53   12.163%   $97.0546   $97.05   $97.05   $97.10  
  Purchase #6 $241.28   8.603%   $262.0373   $262.04   $262.05   $262.00  
  Purchase #7 $196.39   12.441%   $220.8229   $220.82   $220.80   $220.80  
  7 purchase totals = $996.83       $1,091.2384   $1,091.24   $1,091.25   $1,091.10