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 $187.43   5.807%   $198.3141   $198.31   $198.30   $198.30  
  Purchase #2 $46.79   12.384%   $52.5845   $52.58   $52.60   $52.60  
  Purchase #3 $179.39   12.828%   $202.4021   $202.40   $202.40   $202.40  
  Purchase #4 $114.89   13.217%   $130.075   $130.08   $130.10   $130.10  
  Purchase #5 $117.35   8.377%   $127.1804   $127.18   $127.20   $127.20  
  Purchase #6 $191.46   12.562%   $215.5112   $215.51   $215.50   $215.50  
  Purchase #7 $93.39   4.687%   $97.7672   $97.77   $97.75   $97.80  
  7 purchase totals = $930.70       $1,023.8345   $1,023.83   $1,023.85   $1,023.90