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 $64.77   13.166%   $73.2976   $73.30   $73.30   $73.30  
  Purchase #2 $75.34   7.643%   $81.0982   $81.10   $81.10   $81.10  
  Purchase #3 $187.44   13.113%   $212.019   $212.02   $212.00   $212.00  
  Purchase #4 $113.74   9.566%   $124.6204   $124.62   $124.60   $124.60  
  Purchase #5 $156.89   6.312%   $166.7929   $166.79   $166.80   $166.80  
  Purchase #6 $207.37   8.240%   $224.4573   $224.46   $224.45   $224.50  
  Purchase #7 $135.75   4.222%   $141.4814   $141.48   $141.50   $141.50  
  7 purchase totals = $941.30       $1,023.7668   $1,023.77   $1,023.75   $1,023.80