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 $110.67   13.269%   $125.3548   $125.35   $125.35   $125.40  
  Purchase #2 $54.53   8.751%   $59.3019   $59.30   $59.30   $59.30  
  Purchase #3 $121.77   8.499%   $132.1192   $132.12   $132.10   $132.10  
  Purchase #4 $31.73   8.220%   $34.3382   $34.34   $34.35   $34.30  
  Purchase #5 $91.65   13.836%   $104.3307   $104.33   $104.35   $104.30  
  Purchase #6 $136.86   6.457%   $145.6971   $145.70   $145.70   $145.70  
  Purchase #7 $143.42   8.247%   $155.2478   $155.25   $155.25   $155.20  
  7 purchase totals = $690.63       $756.3897   $756.39   $756.40   $756.30