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 $58.34   8.523%   $63.3123   $63.31   $63.30   $63.30  
  Purchase #2 $79.70   7.254%   $85.4814   $85.48   $85.50   $85.50  
  Purchase #3 $168.77   8.546%   $183.1931   $183.19   $183.20   $183.20  
  Purchase #4 $60.94   5.444%   $64.2576   $64.26   $64.25   $64.30  
  Purchase #5 $41.27   9.253%   $45.0887   $45.09   $45.10   $45.10  
  Purchase #6 $160.80   4.697%   $168.3528   $168.35   $168.35   $168.40  
  Purchase #7 $141.33   8.290%   $153.0463   $153.05   $153.05   $153.00  
  7 purchase totals = $711.15       $762.7322   $762.73   $762.75   $762.80