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 $63.37   4.457%   $66.1944   $66.19   $66.20   $66.20  
  Purchase #2 $87.56   11.450%   $97.5856   $97.59   $97.60   $97.60  
  Purchase #3 $146.74   9.397%   $160.5292   $160.53   $160.55   $160.50  
  Purchase #4 $187.70   3.232%   $193.7665   $193.77   $193.75   $193.80  
  Purchase #5 $122.43   5.521%   $129.1894   $129.19   $129.20   $129.20  
  Purchase #6 $98.55   7.544%   $105.9846   $105.98   $106.00   $106.00  
  Purchase #7 $222.33   11.819%   $248.6072   $248.61   $248.60   $248.60  
  7 purchase totals = $928.68       $1,001.8569   $1,001.86   $1,001.90   $1,001.90