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 $84.86   13.612%   $96.4111   $96.41   $96.40   $96.40  
  Purchase #2 $146.39   5.774%   $154.8426   $154.84   $154.85   $154.80  
  Purchase #3 $202.34   7.437%   $217.388   $217.39   $217.40   $217.40  
  Purchase #4 $231.64   9.615%   $253.9122   $253.91   $253.90   $253.90  
  Purchase #5 $112.89   9.700%   $123.8403   $123.84   $123.85   $123.80  
  Purchase #6 $148.30   10.538%   $163.9279   $163.93   $163.95   $163.90  
  Purchase #7 $228.57   5.309%   $240.7048   $240.70   $240.70   $240.70  
  7 purchase totals = $1,154.99       $1,251.0269   $1,251.02   $1,251.05   $1,250.90