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 $183.78   12.823%   $207.3461   $207.35   $207.35   $207.30  
  Purchase #2 $215.43   7.833%   $232.3046   $232.30   $232.30   $232.30  
  Purchase #3 $100.31   5.652%   $105.9795   $105.98   $106.00   $106.00  
  Purchase #4 $202.81   13.489%   $230.167   $230.17   $230.15   $230.20  
  Purchase #5 $239.62   12.457%   $269.4695   $269.47   $269.45   $269.50  
  Purchase #6 $83.96   5.142%   $88.2772   $88.28   $88.30   $88.30  
  Purchase #7 $249.50   3.823%   $259.0384   $259.04   $259.05   $259.00  
  7 purchase totals = $1,275.41       $1,392.5823   $1,392.59   $1,392.60   $1,392.60