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 $63.48   11.268%   $70.6329   $70.63   $70.65   $70.60  
  Purchase #2 $91.26   10.485%   $100.8286   $100.83   $100.85   $100.80  
  Purchase #3 $91.27   12.394%   $102.582   $102.58   $102.60   $102.60  
  Purchase #4 $246.99   12.374%   $277.5525   $277.55   $277.55   $277.60  
  Purchase #5 $176.39   6.241%   $187.3985   $187.40   $187.40   $187.40  
  Purchase #6 $189.37   12.676%   $213.3745   $213.37   $213.35   $213.40  
  Purchase #7 $92.32   11.406%   $102.85   $102.85   $102.85   $102.90  
  7 purchase totals = $951.08       $1,055.2190   $1,055.21   $1,055.25   $1,055.30