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 $98.79   3.446%   $102.1943   $102.19   $102.20   $102.20  
  Purchase #2 $53.28   4.814%   $55.8449   $55.84   $55.85   $55.80  
  Purchase #3 $72.88   4.183%   $75.9286   $75.93   $75.95   $75.90  
  Purchase #4 $105.46   3.160%   $108.7925   $108.79   $108.80   $108.80  
  Purchase #5 $49.82   3.638%   $51.6325   $51.63   $51.65   $51.60  
  Purchase #6 $241.90   5.705%   $255.7004   $255.70   $255.70   $255.70  
  Purchase #7 $248.96   6.533%   $265.2246   $265.22   $265.20   $265.20  
  7 purchase totals = $871.09       $915.3178   $915.30   $915.35   $915.20