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 $104.97   10.250%   $115.7294   $115.73   $115.75   $115.70  
  Purchase #2 $167.79   12.679%   $189.0641   $189.06   $189.05   $189.10  
  Purchase #3 $163.47   8.522%   $177.4009   $177.40   $177.40   $177.40  
  Purchase #4 $103.39   4.826%   $108.3796   $108.38   $108.40   $108.40  
  Purchase #5 $80.82   7.868%   $87.1789   $87.18   $87.20   $87.20  
  Purchase #6 $119.92   12.289%   $134.657   $134.66   $134.65   $134.70  
  Purchase #7 $204.59   7.663%   $220.2677   $220.27   $220.25   $220.30  
  7 purchase totals = $944.95       $1,032.6776   $1,032.68   $1,032.70   $1,032.80