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 $226.60   9.203%   $247.454   $247.45   $247.45   $247.50  
  Purchase #2 $96.96   11.719%   $108.3227   $108.32   $108.30   $108.30  
  Purchase #3 $150.37   10.359%   $165.9468   $165.95   $165.95   $165.90  
  Purchase #4 $62.52   6.866%   $66.8126   $66.81   $66.80   $66.80  
  Purchase #5 $113.73   4.699%   $119.0742   $119.07   $119.05   $119.10  
  Purchase #6 $138.80   13.330%   $157.302   $157.30   $157.30   $157.30  
  Purchase #7 $178.67   10.642%   $197.6841   $197.68   $197.70   $197.70  
  7 purchase totals = $967.65       $1,062.5964   $1,062.58   $1,062.55   $1,062.60