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 $59.79   11.753%   $66.8171   $66.82   $66.80   $66.80  
  Purchase #2 $64.95   12.348%   $72.97   $72.97   $72.95   $73.00  
  Purchase #3 $191.49   8.379%   $207.5349   $207.53   $207.55   $207.50  
  Purchase #4 $137.46   7.472%   $147.731   $147.73   $147.75   $147.70  
  Purchase #5 $36.29   13.713%   $41.2664   $41.27   $41.25   $41.30  
  Purchase #6 $248.27   9.512%   $271.8854   $271.89   $271.90   $271.90  
  Purchase #7 $219.34   13.323%   $248.5627   $248.56   $248.55   $248.60  
  7 purchase totals = $957.59       $1,056.7675   $1,056.77   $1,056.75   $1,056.80