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 $168.79   13.466%   $191.5193   $191.52   $191.50   $191.50  
  Purchase #2 $203.57   7.781%   $219.4098   $219.41   $219.40   $219.40  
  Purchase #3 $77.34   3.231%   $79.8389   $79.84   $79.85   $79.80  
  Purchase #4 $61.99   6.448%   $65.9871   $65.99   $66.00   $66.00  
  Purchase #5 $55.58   12.313%   $62.4236   $62.42   $62.40   $62.40  
  Purchase #6 $174.99   10.804%   $193.8959   $193.90   $193.90   $193.90  
  Purchase #7 $57.26   9.318%   $62.5955   $62.60   $62.60   $62.60  
  7 purchase totals = $799.52       $875.6701   $875.68   $875.65   $875.60