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 $240.73   13.869%   $274.1168   $274.12   $274.10   $274.10  
  Purchase #2 $25.68   3.665%   $26.6212   $26.62   $26.60   $26.60  
  Purchase #3 $135.37   13.488%   $153.6287   $153.63   $153.65   $153.60  
  Purchase #4 $140.91   10.275%   $155.3885   $155.39   $155.40   $155.40  
  Purchase #5 $159.99   5.852%   $169.3526   $169.35   $169.35   $169.40  
  Purchase #6 $231.26   4.202%   $240.9775   $240.98   $241.00   $241.00  
  Purchase #7 $143.35   7.507%   $154.1113   $154.11   $154.10   $154.10  
  7 purchase totals = $1,077.29       $1,174.1966   $1,174.20   $1,174.20   $1,174.20