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 $236.59   10.221%   $260.7719   $260.77   $260.75   $260.80  
  Purchase #2 $169.71   8.387%   $183.9436   $183.94   $183.95   $183.90  
  Purchase #3 $28.46   4.235%   $29.6653   $29.67   $29.65   $29.70  
  Purchase #4 $150.40   12.286%   $168.8781   $168.88   $168.90   $168.90  
  Purchase #5 $184.28   3.860%   $191.3932   $191.39   $191.40   $191.40  
  Purchase #6 $156.86   12.704%   $176.7875   $176.79   $176.80   $176.80  
  Purchase #7 $71.77   13.260%   $81.2867   $81.29   $81.30   $81.30  
  7 purchase totals = $998.07       $1,092.7263   $1,092.73   $1,092.75   $1,092.80