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 $68.63   7.310%   $73.6469   $73.65   $73.65   $73.60  
  Purchase #2 $138.63   12.132%   $155.4486   $155.45   $155.45   $155.40  
  Purchase #3 $46.29   5.283%   $48.7355   $48.74   $48.75   $48.70  
  Purchase #4 $151.32   7.531%   $162.7159   $162.72   $162.70   $162.70  
  Purchase #5 $219.76   9.852%   $241.4108   $241.41   $241.40   $241.40  
  Purchase #6 $183.29   8.803%   $199.425   $199.43   $199.45   $199.40  
  Purchase #7 $240.34   13.825%   $273.567   $273.57   $273.55   $273.60  
  7 purchase totals = $1,048.26       $1,154.9497   $1,154.97   $1,154.95   $1,154.80