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 $14.72   13.103%   $16.6488   $16.65   $16.65   $16.60  
  Purchase #2 $191.41   5.507%   $201.9509   $201.95   $201.95   $202.00  
  Purchase #3 $198.52   7.765%   $213.9351   $213.94   $213.95   $213.90  
  Purchase #4 $204.69   10.579%   $226.3442   $226.34   $226.35   $226.30  
  Purchase #5 $250.72   9.871%   $275.4686   $275.47   $275.45   $275.50  
  Purchase #6 $115.86   7.485%   $124.5321   $124.53   $124.55   $124.50  
  Purchase #7 $196.25   3.532%   $203.1816   $203.18   $203.20   $203.20  
  7 purchase totals = $1,172.17       $1,262.0613   $1,262.06   $1,262.10   $1,262.00