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 $165.84   11.102%   $184.2516   $184.25   $184.25   $184.30  
  Purchase #2 $19.86   9.649%   $21.7763   $21.78   $21.80   $21.80  
  Purchase #3 $179.81   6.586%   $191.6523   $191.65   $191.65   $191.70  
  Purchase #4 $171.49   12.291%   $192.5678   $192.57   $192.55   $192.60  
  Purchase #5 $195.37   7.708%   $210.4291   $210.43   $210.45   $210.40  
  Purchase #6 $206.38   11.506%   $230.1261   $230.13   $230.15   $230.10  
  Purchase #7 $26.70   11.710%   $29.8266   $29.83   $29.85   $29.80  
  7 purchase totals = $965.45       $1,060.6298   $1,060.64   $1,060.70   $1,060.70