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 $61.94   9.254%   $67.6719   $67.67   $67.65   $67.70  
  Purchase #2 $29.49   10.718%   $32.6507   $32.65   $32.65   $32.70  
  Purchase #3 $108.44   9.617%   $118.8687   $118.87   $118.85   $118.90  
  Purchase #4 $190.73   4.708%   $199.7096   $199.71   $199.70   $199.70  
  Purchase #5 $83.93   6.808%   $89.644   $89.64   $89.65   $89.60  
  Purchase #6 $194.70   8.699%   $211.637   $211.64   $211.65   $211.60  
  Purchase #7 $13.88   8.288%   $15.0304   $15.03   $15.05   $15.00  
  7 purchase totals = $683.11       $735.2123   $735.21   $735.20   $735.20