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 $173.87   11.290%   $193.4999   $193.50   $193.50   $193.50  
  Purchase #2 $134.33   13.837%   $152.9172   $152.92   $152.90   $152.90  
  Purchase #3 $143.48   12.484%   $161.392   $161.39   $161.40   $161.40  
  Purchase #4 $69.98   7.525%   $75.246   $75.25   $75.25   $75.20  
  Purchase #5 $181.79   5.235%   $191.3067   $191.31   $191.30   $191.30  
  Purchase #6 $210.40   3.423%   $217.602   $217.60   $217.60   $217.60  
  Purchase #7 $79.41   7.399%   $85.2855   $85.29   $85.30   $85.30  
  7 purchase totals = $993.26       $1,077.2493   $1,077.26   $1,077.25   $1,077.20