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 $94.96   9.828%   $104.2927   $104.29   $104.30   $104.30  
  Purchase #2 $161.55   7.771%   $174.1041   $174.10   $174.10   $174.10  
  Purchase #3 $241.91   12.708%   $272.6519   $272.65   $272.65   $272.70  
  Purchase #4 $177.48   4.351%   $185.2022   $185.20   $185.20   $185.20  
  Purchase #5 $117.49   5.420%   $123.858   $123.86   $123.85   $123.90  
  Purchase #6 $111.25   9.109%   $121.3838   $121.38   $121.40   $121.40  
  Purchase #7 $239.67   11.310%   $266.7767   $266.78   $266.80   $266.80  
  7 purchase totals = $1,144.31       $1,248.2694   $1,248.26   $1,248.30   $1,248.40