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 $31.94   3.417%   $33.0314   $33.03   $33.05   $33.00  
  Purchase #2 $93.65   4.323%   $97.6985   $97.70   $97.70   $97.70  
  Purchase #3 $108.91   9.506%   $119.263   $119.26   $119.25   $119.30  
  Purchase #4 $246.64   12.281%   $276.9299   $276.93   $276.95   $276.90  
  Purchase #5 $187.77   5.276%   $197.6767   $197.68   $197.70   $197.70  
  Purchase #6 $158.85   6.656%   $169.4231   $169.42   $169.40   $169.40  
  Purchase #7 $119.47   11.281%   $132.9474   $132.95   $132.95   $132.90  
  7 purchase totals = $947.23       $1,026.9700   $1,026.97   $1,027.00   $1,026.90