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 $95.94   4.636%   $100.3878   $100.39   $100.40   $100.40  
  Purchase #2 $231.50   13.756%   $263.3451   $263.35   $263.35   $263.30  
  Purchase #3 $249.39   12.301%   $280.0675   $280.07   $280.05   $280.10  
  Purchase #4 $170.94   7.842%   $184.3451   $184.35   $184.35   $184.30  
  Purchase #5 $214.32   8.753%   $233.0794   $233.08   $233.10   $233.10  
  Purchase #6 $152.70   10.485%   $168.7106   $168.71   $168.70   $168.70  
  Purchase #7 $207.51   3.301%   $214.3599   $214.36   $214.35   $214.40  
  7 purchase totals = $1,322.30       $1,444.2954   $1,444.31   $1,444.30   $1,444.30