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 $53.44   9.470%   $58.5008   $58.50   $58.50   $58.50  
  Purchase #2 $131.50   3.541%   $136.1564   $136.16   $136.15   $136.20  
  Purchase #3 $198.68   11.196%   $220.9242   $220.92   $220.90   $220.90  
  Purchase #4 $62.69   7.458%   $67.3654   $67.37   $67.35   $67.40  
  Purchase #5 $218.60   11.625%   $244.0123   $244.01   $244.00   $244.00  
  Purchase #6 $88.68   6.701%   $94.6224   $94.62   $94.60   $94.60  
  Purchase #7 $244.49   12.537%   $275.1417   $275.14   $275.15   $275.10  
  7 purchase totals = $998.08       $1,096.7232   $1,096.72   $1,096.65   $1,096.70