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 $36.44   13.130%   $41.2246   $41.22   $41.20   $41.20  
  Purchase #2 $219.90   12.474%   $247.3303   $247.33   $247.35   $247.30  
  Purchase #3 $41.90   12.653%   $47.2016   $47.20   $47.20   $47.20  
  Purchase #4 $127.29   4.499%   $133.0168   $133.02   $133.00   $133.00  
  Purchase #5 $34.79   10.695%   $38.5108   $38.51   $38.50   $38.50  
  Purchase #6 $217.36   7.555%   $233.7815   $233.78   $233.80   $233.80  
  Purchase #7 $162.58   13.692%   $184.8405   $184.84   $184.85   $184.80  
  7 purchase totals = $840.26       $925.9061   $925.90   $925.90   $925.80