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 $126.68   13.198%   $143.3992   $143.40   $143.40   $143.40  
  Purchase #2 $230.89   6.401%   $245.6693   $245.67   $245.65   $245.70  
  Purchase #3 $199.33   4.292%   $207.8852   $207.89   $207.90   $207.90  
  Purchase #4 $52.91   3.157%   $54.5804   $54.58   $54.60   $54.60  
  Purchase #5 $170.31   11.767%   $190.3504   $190.35   $190.35   $190.40  
  Purchase #6 $116.65   12.478%   $131.2056   $131.21   $131.20   $131.20  
  Purchase #7 $54.49   11.736%   $60.8849   $60.88   $60.90   $60.90  
  7 purchase totals = $951.26       $1,033.9750   $1,033.98   $1,034.00   $1,034.10