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 $83.96   11.477%   $93.5961   $93.60   $93.60   $93.60  
  Purchase #2 $189.95   7.858%   $204.8763   $204.88   $204.90   $204.90  
  Purchase #3 $123.67   8.820%   $134.5777   $134.58   $134.60   $134.60  
  Purchase #4 $230.71   13.833%   $262.6241   $262.62   $262.60   $262.60  
  Purchase #5 $140.27   5.294%   $147.6959   $147.70   $147.70   $147.70  
  Purchase #6 $161.63   13.823%   $183.9721   $183.97   $183.95   $184.00  
  Purchase #7 $240.66   11.285%   $267.8185   $267.82   $267.80   $267.80  
  7 purchase totals = $1,170.85       $1,295.1607   $1,295.17   $1,295.15   $1,295.20