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 $178.33   10.534%   $197.1153   $197.12   $197.10   $197.10  
  Purchase #2 $190.77   8.388%   $206.7718   $206.77   $206.75   $206.80  
  Purchase #3 $127.92   7.582%   $137.6189   $137.62   $137.60   $137.60  
  Purchase #4 $245.59   5.738%   $259.682   $259.68   $259.70   $259.70  
  Purchase #5 $49.70   8.818%   $54.0825   $54.08   $54.10   $54.10  
  Purchase #6 $214.98   12.658%   $242.1922   $242.19   $242.20   $242.20  
  Purchase #7 $123.94   5.257%   $130.4555   $130.46   $130.45   $130.50  
  7 purchase totals = $1,131.23       $1,227.9182   $1,227.92   $1,227.90   $1,228.00