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 $173.69   7.373%   $186.4962   $186.50   $186.50   $186.50  
  Purchase #2 $224.96   10.667%   $248.9565   $248.96   $248.95   $249.00  
  Purchase #3 $67.59   6.428%   $71.9347   $71.93   $71.95   $71.90  
  Purchase #4 $219.58   12.798%   $247.6818   $247.68   $247.70   $247.70  
  Purchase #5 $181.82   11.847%   $203.3602   $203.36   $203.35   $203.40  
  Purchase #6 $231.28   10.257%   $255.0024   $255.00   $255.00   $255.00  
  Purchase #7 $47.61   5.455%   $50.2071   $50.21   $50.20   $50.20  
  7 purchase totals = $1,146.53       $1,263.6389   $1,263.64   $1,263.65   $1,263.70