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 $204.79   6.586%   $218.2775   $218.28   $218.30   $218.30  
  Purchase #2 $150.62   9.144%   $164.3927   $164.39   $164.40   $164.40  
  Purchase #3 $59.43   8.296%   $64.3603   $64.36   $64.35   $64.40  
  Purchase #4 $38.57   4.593%   $40.3415   $40.34   $40.35   $40.30  
  Purchase #5 $99.81   5.664%   $105.4632   $105.46   $105.45   $105.50  
  Purchase #6 $214.60   9.507%   $235.002   $235.00   $235.00   $235.00  
  Purchase #7 $227.51   8.560%   $246.9849   $246.98   $247.00   $247.00  
  7 purchase totals = $995.33       $1,074.8221   $1,074.81   $1,074.85   $1,074.90