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 $69.87   7.861%   $75.3625   $75.36   $75.35   $75.40  
  Purchase #2 $160.80   8.606%   $174.6384   $174.64   $174.65   $174.60  
  Purchase #3 $208.78   4.512%   $218.2002   $218.20   $218.20   $218.20  
  Purchase #4 $53.55   3.330%   $55.3332   $55.33   $55.35   $55.30  
  Purchase #5 $150.82   13.871%   $171.7402   $171.74   $171.75   $171.70  
  Purchase #6 $165.41   8.125%   $178.8496   $178.85   $178.85   $178.80  
  Purchase #7 $140.99   7.845%   $152.0507   $152.05   $152.05   $152.10  
  7 purchase totals = $950.22       $1,026.1748   $1,026.17   $1,026.20   $1,026.10