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 $209.44   11.717%   $233.9801   $233.98   $234.00   $234.00  
  Purchase #2 $92.81   3.328%   $95.8987   $95.90   $95.90   $95.90  
  Purchase #3 $93.77   13.247%   $106.1917   $106.19   $106.20   $106.20  
  Purchase #4 $130.52   6.790%   $139.3823   $139.38   $139.40   $139.40  
  Purchase #5 $137.72   10.366%   $151.9961   $152.00   $152.00   $152.00  
  Purchase #6 $192.40   3.213%   $198.5818   $198.58   $198.60   $198.60  
  Purchase #7 $150.87   7.213%   $161.7523   $161.75   $161.75   $161.80  
  7 purchase totals = $1,007.53       $1,087.7830   $1,087.78   $1,087.85   $1,087.90