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 $169.59   8.637%   $184.2375   $184.24   $184.25   $184.20  
  Purchase #2 $22.47   5.252%   $23.6501   $23.65   $23.65   $23.70  
  Purchase #3 $125.44   5.809%   $132.7268   $132.73   $132.75   $132.70  
  Purchase #4 $237.58   11.300%   $264.4265   $264.43   $264.45   $264.40  
  Purchase #5 $199.46   7.831%   $215.0797   $215.08   $215.10   $215.10  
  Purchase #6 $179.47   10.287%   $197.9321   $197.93   $197.95   $197.90  
  Purchase #7 $181.39   4.845%   $190.1783   $190.18   $190.20   $190.20  
  7 purchase totals = $1,115.40       $1,208.2310   $1,208.24   $1,208.35   $1,208.20