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 $183.92   11.294%   $204.6919   $204.69   $204.70   $204.70  
  Purchase #2 $19.56   3.343%   $20.2139   $20.21   $20.20   $20.20  
  Purchase #3 $139.41   4.219%   $145.2917   $145.29   $145.30   $145.30  
  Purchase #4 $44.99   6.703%   $48.0057   $48.01   $48.00   $48.00  
  Purchase #5 $116.75   6.802%   $124.6913   $124.69   $124.70   $124.70  
  Purchase #6 $182.92   10.654%   $202.4083   $202.41   $202.40   $202.40  
  Purchase #7 $230.70   12.283%   $259.0369   $259.04   $259.05   $259.00  
  7 purchase totals = $918.25       $1,004.3397   $1,004.34   $1,004.35   $1,004.30