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 $197.94   3.362%   $204.5947   $204.59   $204.60   $204.60  
  Purchase #2 $150.42   8.558%   $163.2929   $163.29   $163.30   $163.30  
  Purchase #3 $92.42   6.671%   $98.5853   $98.59   $98.60   $98.60  
  Purchase #4 $237.37   9.810%   $260.656   $260.66   $260.65   $260.70  
  Purchase #5 $52.84   8.592%   $57.38   $57.38   $57.40   $57.40  
  Purchase #6 $44.70   8.452%   $48.478   $48.48   $48.50   $48.50  
  Purchase #7 $206.32   13.123%   $233.3954   $233.40   $233.40   $233.40  
  7 purchase totals = $982.01       $1,066.3823   $1,066.39   $1,066.45   $1,066.50