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 $154.82   9.275%   $169.1796   $169.18   $169.20   $169.20  
  Purchase #2 $223.63   8.823%   $243.3609   $243.36   $243.35   $243.40  
  Purchase #3 $143.80   5.796%   $152.1346   $152.13   $152.15   $152.10  
  Purchase #4 $38.89   6.653%   $41.4774   $41.48   $41.50   $41.50  
  Purchase #5 $148.30   3.577%   $153.6047   $153.60   $153.60   $153.60  
  Purchase #6 $11.32   3.649%   $11.7331   $11.73   $11.75   $11.70  
  Purchase #7 $244.48   9.863%   $268.5931   $268.59   $268.60   $268.60  
  7 purchase totals = $965.24       $1,040.0834   $1,040.07   $1,040.15   $1,040.10