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 $171.74   7.282%   $184.2461   $184.25   $184.25   $184.20  
  Purchase #2 $189.26   11.454%   $210.9378   $210.94   $210.95   $210.90  
  Purchase #3 $20.33   4.227%   $21.1893   $21.19   $21.20   $21.20  
  Purchase #4 $190.73   8.821%   $207.5543   $207.55   $207.55   $207.60  
  Purchase #5 $78.80   10.854%   $87.353   $87.35   $87.35   $87.40  
  Purchase #6 $241.30   11.649%   $269.409   $269.41   $269.40   $269.40  
  Purchase #7 $51.95   3.811%   $53.9298   $53.93   $53.95   $53.90  
  7 purchase totals = $944.11       $1,034.6193   $1,034.62   $1,034.65   $1,034.60