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 $219.67   12.698%   $247.5637   $247.56   $247.55   $247.60  
  Purchase #2 $63.74   3.186%   $65.7708   $65.77   $65.75   $65.80  
  Purchase #3 $222.67   10.153%   $245.2777   $245.28   $245.30   $245.30  
  Purchase #4 $54.62   6.374%   $58.1015   $58.10   $58.10   $58.10  
  Purchase #5 $166.81   10.519%   $184.3567   $184.36   $184.35   $184.40  
  Purchase #6 $139.57   9.428%   $152.7287   $152.73   $152.75   $152.70  
  Purchase #7 $106.26   6.172%   $112.8184   $112.82   $112.80   $112.80  
  7 purchase totals = $973.34       $1,066.6175   $1,066.62   $1,066.60   $1,066.70