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 $32.81   8.579%   $35.6248   $35.62   $35.60   $35.60  
  Purchase #2 $92.29   5.615%   $97.4721   $97.47   $97.45   $97.50  
  Purchase #3 $118.52   3.279%   $122.4063   $122.41   $122.40   $122.40  
  Purchase #4 $184.83   9.564%   $202.5071   $202.51   $202.50   $202.50  
  Purchase #5 $201.51   6.237%   $214.0782   $214.08   $214.10   $214.10  
  Purchase #6 $72.48   7.427%   $77.8631   $77.86   $77.85   $77.90  
  Purchase #7 $177.39   8.409%   $192.3067   $192.31   $192.30   $192.30  
  7 purchase totals = $879.83       $942.2583   $942.26   $942.20   $942.30