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 $86.71   8.107%   $93.7396   $93.74   $93.75   $93.70  
  Purchase #2 $188.96   5.871%   $200.0538   $200.05   $200.05   $200.10  
  Purchase #3 $48.68   6.603%   $51.8943   $51.89   $51.90   $51.90  
  Purchase #4 $125.88   11.302%   $140.107   $140.11   $140.10   $140.10  
  Purchase #5 $55.38   7.658%   $59.621   $59.62   $59.60   $59.60  
  Purchase #6 $35.64   6.171%   $37.8393   $37.84   $37.85   $37.80  
  Purchase #7 $192.88   9.807%   $211.7957   $211.80   $211.80   $211.80  
  7 purchase totals = $734.13       $795.0507   $795.05   $795.05   $795.00