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 $194.99   8.328%   $211.2288   $211.23   $211.25   $211.20  
  Purchase #2 $91.80   10.514%   $101.4519   $101.45   $101.45   $101.50  
  Purchase #3 $60.38   9.547%   $66.1445   $66.14   $66.15   $66.10  
  Purchase #4 $24.38   8.630%   $26.484   $26.48   $26.50   $26.50  
  Purchase #5 $181.65   3.430%   $187.8806   $187.88   $187.90   $187.90  
  Purchase #6 $157.56   9.460%   $172.4652   $172.47   $172.45   $172.50  
  Purchase #7 $174.79   9.586%   $191.5454   $191.55   $191.55   $191.50  
  7 purchase totals = $885.55       $957.2004   $957.20   $957.25   $957.20