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 $56.79   11.605%   $63.3805   $63.38   $63.40   $63.40  
  Purchase #2 $209.87   13.327%   $237.8394   $237.84   $237.85   $237.80  
  Purchase #3 $224.90   12.556%   $253.1384   $253.14   $253.15   $253.10  
  Purchase #4 $7.58   11.351%   $8.4404   $8.44   $8.45   $8.40  
  Purchase #5 $186.72   7.801%   $201.286   $201.29   $201.30   $201.30  
  Purchase #6 $201.64   5.822%   $213.3795   $213.38   $213.40   $213.40  
  Purchase #7 $80.76   6.188%   $85.7574   $85.76   $85.75   $85.80  
  7 purchase totals = $968.26       $1,063.2216   $1,063.23   $1,063.30   $1,063.20