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 $68.88   5.271%   $72.5107   $72.51   $72.50   $72.50  
  Purchase #2 $18.91   9.764%   $20.7564   $20.76   $20.75   $20.80  
  Purchase #3 $167.26   3.279%   $172.7445   $172.74   $172.75   $172.70  
  Purchase #4 $201.99   12.581%   $227.4024   $227.40   $227.40   $227.40  
  Purchase #5 $227.58   3.338%   $235.1766   $235.18   $235.20   $235.20  
  Purchase #6 $110.84   7.629%   $119.296   $119.30   $119.30   $119.30  
  Purchase #7 $238.76   12.362%   $268.2755   $268.28   $268.30   $268.30  
  7 purchase totals = $1,034.22       $1,116.1621   $1,116.17   $1,116.20   $1,116.20