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 $184.69   10.324%   $203.7574   $203.76   $203.75   $203.80  
  Purchase #2 $242.72   9.200%   $265.0502   $265.05   $265.05   $265.10  
  Purchase #3 $33.51   12.301%   $37.6321   $37.63   $37.65   $37.60  
  Purchase #4 $41.96   7.749%   $45.2115   $45.21   $45.20   $45.20  
  Purchase #5 $147.34   6.755%   $157.2928   $157.29   $157.30   $157.30  
  Purchase #6 $69.60   5.735%   $73.5916   $73.59   $73.60   $73.60  
  Purchase #7 $248.67   4.325%   $259.425   $259.43   $259.45   $259.40  
  7 purchase totals = $968.49       $1,041.9606   $1,041.96   $1,042.00   $1,042.00