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 $33.59   9.702%   $36.8489   $36.85   $36.85   $36.80  
  Purchase #2 $175.37   11.515%   $195.5639   $195.56   $195.55   $195.60  
  Purchase #3 $52.48   6.558%   $55.9216   $55.92   $55.90   $55.90  
  Purchase #4 $168.26   12.609%   $189.4759   $189.48   $189.50   $189.50  
  Purchase #5 $215.58   6.606%   $229.8212   $229.82   $229.80   $229.80  
  Purchase #6 $229.90   11.451%   $256.2258   $256.23   $256.25   $256.20  
  Purchase #7 $45.43   3.651%   $47.0886   $47.09   $47.10   $47.10  
  7 purchase totals = $920.61       $1,010.9459   $1,010.95   $1,010.95   $1,010.90