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 $88.52   11.336%   $98.5546   $98.55   $98.55   $98.60  
  Purchase #2 $206.68   11.157%   $229.7393   $229.74   $229.75   $229.70  
  Purchase #3 $207.95   6.541%   $221.552   $221.55   $221.55   $221.60  
  Purchase #4 $129.93   8.742%   $141.2885   $141.29   $141.30   $141.30  
  Purchase #5 $101.81   3.567%   $105.4416   $105.44   $105.45   $105.40  
  Purchase #6 $216.76   4.264%   $226.0026   $226.00   $226.00   $226.00  
  Purchase #7 $86.50   6.552%   $92.1675   $92.17   $92.15   $92.20  
  7 purchase totals = $1,038.15       $1,114.7461   $1,114.74   $1,114.75   $1,114.80