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 $244.93   8.492%   $265.7295   $265.73   $265.75   $265.70  
  Purchase #2 $236.84   8.527%   $257.0353   $257.04   $257.05   $257.00  
  Purchase #3 $189.94   11.119%   $211.0594   $211.06   $211.05   $211.10  
  Purchase #4 $38.45   10.622%   $42.5342   $42.53   $42.55   $42.50  
  Purchase #5 $152.59   13.410%   $173.0523   $173.05   $173.05   $173.10  
  Purchase #6 $206.54   6.514%   $219.994   $219.99   $220.00   $220.00  
  Purchase #7 $99.35   6.250%   $105.5594   $105.56   $105.55   $105.60  
  7 purchase totals = $1,168.64       $1,274.9641   $1,274.96   $1,275.00   $1,275.00