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 $167.55   3.244%   $172.9853   $172.99   $173.00   $173.00  
  Purchase #2 $178.63   8.414%   $193.6599   $193.66   $193.65   $193.70  
  Purchase #3 $53.37   10.385%   $58.9125   $58.91   $58.90   $58.90  
  Purchase #4 $196.95   11.738%   $220.068   $220.07   $220.05   $220.10  
  Purchase #5 $87.58   11.501%   $97.6526   $97.65   $97.65   $97.70  
  Purchase #6 $229.88   6.481%   $244.7785   $244.78   $244.80   $244.80  
  Purchase #7 $39.98   11.461%   $44.5621   $44.56   $44.55   $44.60  
  7 purchase totals = $953.94       $1,032.6189   $1,032.62   $1,032.60   $1,032.80