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 $224.96   13.349%   $254.9899   $254.99   $255.00   $255.00  
  Purchase #2 $232.99   4.305%   $243.0202   $243.02   $243.00   $243.00  
  Purchase #3 $209.30   4.515%   $218.7499   $218.75   $218.75   $218.70  
  Purchase #4 $224.72   3.663%   $232.9515   $232.95   $232.95   $233.00  
  Purchase #5 $206.42   7.198%   $221.2781   $221.28   $221.30   $221.30  
  Purchase #6 $50.65   7.502%   $54.4498   $54.45   $54.45   $54.40  
  Purchase #7 $187.41   12.798%   $211.3947   $211.39   $211.40   $211.40  
  7 purchase totals = $1,336.45       $1,436.8341   $1,436.83   $1,436.85   $1,436.80