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 $175.51   11.837%   $196.2851   $196.29   $196.30   $196.30  
  Purchase #2 $60.67   7.452%   $65.1911   $65.19   $65.20   $65.20  
  Purchase #3 $178.84   13.401%   $202.8063   $202.81   $202.80   $202.80  
  Purchase #4 $147.72   7.160%   $158.2968   $158.30   $158.30   $158.30  
  Purchase #5 $212.77   10.334%   $234.7577   $234.76   $234.75   $234.80  
  Purchase #6 $68.26   6.488%   $72.6887   $72.69   $72.70   $72.70  
  Purchase #7 $242.38   9.190%   $264.6547   $264.65   $264.65   $264.70  
  7 purchase totals = $1,086.15       $1,194.6804   $1,194.69   $1,194.70   $1,194.80