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 $120.43   5.476%   $127.0247   $127.02   $127.00   $127.00  
  Purchase #2 $94.35   13.272%   $106.8721   $106.87   $106.85   $106.90  
  Purchase #3 $32.30   13.393%   $36.6259   $36.63   $36.65   $36.60  
  Purchase #4 $167.92   9.775%   $184.3342   $184.33   $184.35   $184.30  
  Purchase #5 $231.33   3.462%   $239.3386   $239.34   $239.35   $239.30  
  Purchase #6 $95.59   4.731%   $100.1124   $100.11   $100.10   $100.10  
  Purchase #7 $237.68   12.680%   $267.8178   $267.82   $267.80   $267.80  
  7 purchase totals = $979.60       $1,062.1257   $1,062.12   $1,062.10   $1,062.00