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 $88.95   10.702%   $98.4694   $98.47   $98.45   $98.50  
  Purchase #2 $161.84   11.543%   $180.5212   $180.52   $180.50   $180.50  
  Purchase #3 $111.72   13.763%   $127.096   $127.10   $127.10   $127.10  
  Purchase #4 $249.98   8.325%   $270.7908   $270.79   $270.80   $270.80  
  Purchase #5 $158.30   12.341%   $177.8358   $177.84   $177.85   $177.80  
  Purchase #6 $241.83   10.606%   $267.4785   $267.48   $267.50   $267.50  
  Purchase #7 $53.88   11.528%   $60.0913   $60.09   $60.10   $60.10  
  7 purchase totals = $1,066.50       $1,182.2830   $1,182.29   $1,182.30   $1,182.30