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 $239.49   6.224%   $254.3959   $254.40   $254.40   $254.40  
  Purchase #2 $94.77   8.379%   $102.7108   $102.71   $102.70   $102.70  
  Purchase #3 $118.57   8.203%   $128.2963   $128.30   $128.30   $128.30  
  Purchase #4 $200.81   13.605%   $228.1302   $228.13   $228.15   $228.10  
  Purchase #5 $101.60   9.559%   $111.3119   $111.31   $111.30   $111.30  
  Purchase #6 $234.55   12.135%   $263.0126   $263.01   $263.00   $263.00  
  Purchase #7 $81.44   9.778%   $89.4032   $89.40   $89.40   $89.40  
  7 purchase totals = $1,071.23       $1,177.2609   $1,177.26   $1,177.25   $1,177.20