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 $180.80   8.167%   $195.5659   $195.57   $195.55   $195.60  
  Purchase #2 $167.79   10.765%   $185.8526   $185.85   $185.85   $185.90  
  Purchase #3 $161.92   12.148%   $181.59   $181.59   $181.60   $181.60  
  Purchase #4 $123.86   5.113%   $130.193   $130.19   $130.20   $130.20  
  Purchase #5 $204.37   11.528%   $227.9298   $227.93   $227.95   $227.90  
  Purchase #6 $236.77   12.578%   $266.5509   $266.55   $266.55   $266.60  
  Purchase #7 $55.99   5.152%   $58.8746   $58.87   $58.85   $58.90  
  7 purchase totals = $1,131.50       $1,246.5568   $1,246.55   $1,246.55   $1,246.70