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 $232.97   11.612%   $260.0225   $260.02   $260.00   $260.00  
  Purchase #2 $80.45   4.129%   $83.7718   $83.77   $83.75   $83.80  
  Purchase #3 $139.82   7.205%   $149.894   $149.89   $149.90   $149.90  
  Purchase #4 $192.85   6.631%   $205.6379   $205.64   $205.65   $205.60  
  Purchase #5 $218.29   6.555%   $232.5989   $232.60   $232.60   $232.60  
  Purchase #6 $70.65   9.553%   $77.3992   $77.40   $77.40   $77.40  
  Purchase #7 $31.98   6.673%   $34.114   $34.11   $34.10   $34.10  
  7 purchase totals = $967.01       $1,043.4383   $1,043.43   $1,043.40   $1,043.40