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 $195.41   3.157%   $201.5791   $201.58   $201.60   $201.60  
  Purchase #2 $79.55   9.446%   $87.0643   $87.06   $87.05   $87.10  
  Purchase #3 $213.63   12.148%   $239.5818   $239.58   $239.60   $239.60  
  Purchase #4 $154.64   11.462%   $172.3648   $172.36   $172.35   $172.40  
  Purchase #5 $114.80   9.266%   $125.4374   $125.44   $125.45   $125.40  
  Purchase #6 $99.77   4.828%   $104.5869   $104.59   $104.60   $104.60  
  Purchase #7 $131.43   7.427%   $141.1913   $141.19   $141.20   $141.20  
  7 purchase totals = $989.23       $1,071.8056   $1,071.80   $1,071.85   $1,071.90