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 $207.42   12.312%   $232.9576   $232.96   $232.95   $233.00  
  Purchase #2 $36.48   7.221%   $39.1142   $39.11   $39.10   $39.10  
  Purchase #3 $120.68   8.153%   $130.519   $130.52   $130.50   $130.50  
  Purchase #4 $169.83   11.505%   $189.3689   $189.37   $189.35   $189.40  
  Purchase #5 $163.72   6.734%   $174.7449   $174.74   $174.75   $174.70  
  Purchase #6 $140.30   11.521%   $156.464   $156.46   $156.45   $156.50  
  Purchase #7 $161.81   11.629%   $180.6269   $180.63   $180.65   $180.60  
  7 purchase totals = $1,000.24       $1,103.7955   $1,103.79   $1,103.75   $1,103.80