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 $83.82   5.221%   $88.1962   $88.20   $88.20   $88.20  
  Purchase #2 $219.82   3.522%   $227.5621   $227.56   $227.55   $227.60  
  Purchase #3 $244.57   3.813%   $253.8955   $253.90   $253.90   $253.90  
  Purchase #4 $215.27   8.748%   $234.1018   $234.10   $234.10   $234.10  
  Purchase #5 $158.65   5.763%   $167.793   $167.79   $167.80   $167.80  
  Purchase #6 $163.69   4.120%   $170.434   $170.43   $170.45   $170.40  
  Purchase #7 $6.47   7.561%   $6.9592   $6.96   $6.95   $7.00  
  7 purchase totals = $1,092.29       $1,148.9418   $1,148.94   $1,148.95   $1,149.00