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 $188.63   8.413%   $204.4994   $204.50   $204.50   $204.50  
  Purchase #2 $35.77   4.369%   $37.3328   $37.33   $37.35   $37.30  
  Purchase #3 $223.63   5.598%   $236.1488   $236.15   $236.15   $236.10  
  Purchase #4 $188.81   5.258%   $198.7376   $198.74   $198.75   $198.70  
  Purchase #5 $75.69   4.392%   $79.0143   $79.01   $79.00   $79.00  
  Purchase #6 $174.77   5.540%   $184.4523   $184.45   $184.45   $184.50  
  Purchase #7 $169.78   7.283%   $182.1451   $182.15   $182.15   $182.10  
  7 purchase totals = $1,057.08       $1,122.3303   $1,122.33   $1,122.35   $1,122.20