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 $187.97   3.758%   $195.0339   $195.03   $195.05   $195.00  
  Purchase #2 $84.88   3.129%   $87.5359   $87.54   $87.55   $87.50  
  Purchase #3 $161.54   7.768%   $174.0884   $174.09   $174.10   $174.10  
  Purchase #4 $25.87   4.198%   $26.956   $26.96   $26.95   $27.00  
  Purchase #5 $203.27   9.382%   $222.3408   $222.34   $222.35   $222.30  
  Purchase #6 $179.87   12.642%   $202.6092   $202.61   $202.60   $202.60  
  Purchase #7 $143.65   12.369%   $161.4181   $161.42   $161.40   $161.40  
  7 purchase totals = $987.05       $1,069.9823   $1,069.99   $1,070.00   $1,069.90