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 $46.49   4.365%   $48.5193   $48.52   $48.50   $48.50  
  Purchase #2 $186.87   9.483%   $204.5909   $204.59   $204.60   $204.60  
  Purchase #3 $233.31   12.131%   $261.6128   $261.61   $261.60   $261.60  
  Purchase #4 $182.27   12.384%   $204.8423   $204.84   $204.85   $204.80  
  Purchase #5 $167.85   7.121%   $179.8026   $179.80   $179.80   $179.80  
  Purchase #6 $154.44   8.256%   $167.1906   $167.19   $167.20   $167.20  
  Purchase #7 $100.58   6.121%   $106.7365   $106.74   $106.75   $106.70  
  7 purchase totals = $1,071.81       $1,173.2950   $1,173.29   $1,173.30   $1,173.20