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 $93.27   10.721%   $103.2695   $103.27   $103.25   $103.30  
  Purchase #2 $135.97   8.373%   $147.3548   $147.35   $147.35   $147.40  
  Purchase #3 $35.76   8.121%   $38.6641   $38.66   $38.65   $38.70  
  Purchase #4 $189.42   5.385%   $199.6203   $199.62   $199.60   $199.60  
  Purchase #5 $26.67   7.393%   $28.6417   $28.64   $28.65   $28.60  
  Purchase #6 $116.47   9.250%   $127.2435   $127.24   $127.25   $127.20  
  Purchase #7 $205.64   11.312%   $228.902   $228.90   $228.90   $228.90  
  7 purchase totals = $803.20       $873.6959   $873.68   $873.65   $873.70