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 $33.95   6.600%   $36.1907   $36.19   $36.20   $36.20  
  Purchase #2 $214.72   5.173%   $225.8275   $225.83   $225.85   $225.80  
  Purchase #3 $141.27   6.682%   $150.7097   $150.71   $150.70   $150.70  
  Purchase #4 $169.49   9.767%   $186.0441   $186.04   $186.05   $186.00  
  Purchase #5 $95.95   11.380%   $106.8691   $106.87   $106.85   $106.90  
  Purchase #6 $123.47   7.295%   $132.4771   $132.48   $132.50   $132.50  
  Purchase #7 $182.61   7.470%   $196.251   $196.25   $196.25   $196.30  
  7 purchase totals = $961.46       $1,034.3692   $1,034.37   $1,034.40   $1,034.40