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 $68.74   4.219%   $71.6401   $71.64   $71.65   $71.60  
  Purchase #2 $245.52   11.376%   $273.4504   $273.45   $273.45   $273.50  
  Purchase #3 $67.80   9.303%   $74.1074   $74.11   $74.10   $74.10  
  Purchase #4 $195.82   9.704%   $214.8224   $214.82   $214.80   $214.80  
  Purchase #5 $75.98   9.276%   $83.0279   $83.03   $83.05   $83.00  
  Purchase #6 $100.75   3.313%   $104.0878   $104.09   $104.10   $104.10  
  Purchase #7 $168.47   7.351%   $180.8542   $180.85   $180.85   $180.90  
  7 purchase totals = $923.08       $1,001.9902   $1,001.99   $1,002.00   $1,002.00