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 $169.97   8.234%   $183.9653   $183.97   $183.95   $184.00  
  Purchase #2 $135.65   10.799%   $150.2988   $150.30   $150.30   $150.30  
  Purchase #3 $86.48   12.701%   $97.4638   $97.46   $97.45   $97.50  
  Purchase #4 $79.35   5.504%   $83.7174   $83.72   $83.70   $83.70  
  Purchase #5 $189.88   11.294%   $211.325   $211.33   $211.35   $211.30  
  Purchase #6 $136.77   5.586%   $144.41   $144.41   $144.40   $144.40  
  Purchase #7 $178.67   9.761%   $196.11   $196.11   $196.10   $196.10  
  7 purchase totals = $976.77       $1,067.2903   $1,067.30   $1,067.25   $1,067.30