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 $203.29   7.749%   $219.0429   $219.04   $219.05   $219.00  
  Purchase #2 $95.85   6.480%   $102.0611   $102.06   $102.05   $102.10  
  Purchase #3 $241.39   9.475%   $264.2617   $264.26   $264.25   $264.30  
  Purchase #4 $88.69   13.790%   $100.9204   $100.92   $100.90   $100.90  
  Purchase #5 $118.78   12.406%   $133.5158   $133.52   $133.50   $133.50  
  Purchase #6 $131.59   6.432%   $140.0539   $140.05   $140.05   $140.10  
  Purchase #7 $178.88   11.627%   $199.6784   $199.68   $199.70   $199.70  
  7 purchase totals = $1,058.47       $1,159.5342   $1,159.53   $1,159.50   $1,159.60