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 $69.55   11.625%   $77.6352   $77.64   $77.65   $77.60  
  Purchase #2 $141.56   4.104%   $147.3696   $147.37   $147.35   $147.40  
  Purchase #3 $116.45   5.275%   $122.5927   $122.59   $122.60   $122.60  
  Purchase #4 $172.49   9.811%   $189.413   $189.41   $189.40   $189.40  
  Purchase #5 $204.97   4.125%   $213.425   $213.43   $213.45   $213.40  
  Purchase #6 $173.72   8.464%   $188.4237   $188.42   $188.40   $188.40  
  Purchase #7 $45.41   11.726%   $50.7348   $50.73   $50.75   $50.70  
  7 purchase totals = $924.15       $989.5940   $989.59   $989.60   $989.50