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 $191.82   5.716%   $202.7844   $202.78   $202.80   $202.80  
  Purchase #2 $194.46   4.764%   $203.7241   $203.72   $203.70   $203.70  
  Purchase #3 $18.50   6.161%   $19.6398   $19.64   $19.65   $19.60  
  Purchase #4 $227.26   8.800%   $247.2589   $247.26   $247.25   $247.30  
  Purchase #5 $244.83   9.214%   $267.3886   $267.39   $267.40   $267.40  
  Purchase #6 $95.47   7.376%   $102.5119   $102.51   $102.50   $102.50  
  Purchase #7 $203.54   5.656%   $215.0522   $215.05   $215.05   $215.10  
  7 purchase totals = $1,175.88       $1,258.3599   $1,258.35   $1,258.35   $1,258.40