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 $31.77   10.763%   $35.1894   $35.19   $35.20   $35.20  
  Purchase #2 $203.95   4.578%   $213.2868   $213.29   $213.30   $213.30  
  Purchase #3 $155.84   9.530%   $170.6916   $170.69   $170.70   $170.70  
  Purchase #4 $244.62   4.807%   $256.3789   $256.38   $256.40   $256.40  
  Purchase #5 $74.89   13.493%   $84.9949   $84.99   $85.00   $85.00  
  Purchase #6 $209.65   6.505%   $223.2877   $223.29   $223.30   $223.30  
  Purchase #7 $46.97   3.234%   $48.489   $48.49   $48.50   $48.50  
  7 purchase totals = $967.69       $1,032.3183   $1,032.32   $1,032.40   $1,032.40