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 $196.98   4.590%   $206.0214   $206.02   $206.00   $206.00  
  Purchase #2 $71.58   13.190%   $81.0214   $81.02   $81.00   $81.00  
  Purchase #3 $244.78   12.425%   $275.1939   $275.19   $275.20   $275.20  
  Purchase #4 $169.89   12.568%   $191.2418   $191.24   $191.25   $191.20  
  Purchase #5 $44.54   10.656%   $49.2862   $49.29   $49.30   $49.30  
  Purchase #6 $85.86   6.804%   $91.7019   $91.70   $91.70   $91.70  
  Purchase #7 $73.47   11.762%   $82.1115   $82.11   $82.10   $82.10  
  7 purchase totals = $887.10       $976.5781   $976.57   $976.55   $976.50