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 $14.98   11.534%   $16.7078   $16.71   $16.70   $16.70  
  Purchase #2 $98.62   7.638%   $106.1526   $106.15   $106.15   $106.20  
  Purchase #3 $211.99   12.735%   $238.9869   $238.99   $239.00   $239.00  
  Purchase #4 $194.49   11.122%   $216.1212   $216.12   $216.10   $216.10  
  Purchase #5 $26.38   4.468%   $27.5587   $27.56   $27.55   $27.60  
  Purchase #6 $160.94   7.404%   $172.856   $172.86   $172.85   $172.90  
  Purchase #7 $145.29   9.171%   $158.6145   $158.61   $158.60   $158.60  
  7 purchase totals = $852.69       $936.9977   $937.00   $936.95   $937.10