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 $77.52   10.297%   $85.5022   $85.50   $85.50   $85.50  
  Purchase #2 $189.69   11.427%   $211.3659   $211.37   $211.35   $211.40  
  Purchase #3 $91.41   13.357%   $103.6196   $103.62   $103.60   $103.60  
  Purchase #4 $35.99   5.420%   $37.9407   $37.94   $37.95   $37.90  
  Purchase #5 $156.51   3.723%   $162.3369   $162.34   $162.35   $162.30  
  Purchase #6 $195.50   3.259%   $201.8713   $201.87   $201.85   $201.90  
  Purchase #7 $14.97   11.156%   $16.6401   $16.64   $16.65   $16.60  
  7 purchase totals = $761.59       $819.2767   $819.28   $819.25   $819.20