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 $7.72   9.247%   $8.4339   $8.43   $8.45   $8.40  
  Purchase #2 $197.77   9.386%   $216.3327   $216.33   $216.35   $216.30  
  Purchase #3 $48.86   10.119%   $53.8041   $53.80   $53.80   $53.80  
  Purchase #4 $169.76   5.312%   $178.7777   $178.78   $178.80   $178.80  
  Purchase #5 $62.78   6.712%   $66.9938   $66.99   $67.00   $67.00  
  Purchase #6 $205.88   4.767%   $215.6943   $215.69   $215.70   $215.70  
  Purchase #7 $238.25   12.640%   $268.3648   $268.36   $268.35   $268.40  
  7 purchase totals = $931.02       $1,008.4013   $1,008.38   $1,008.45   $1,008.40