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 $92.52   11.408%   $103.0747   $103.07   $103.05   $103.10  
  Purchase #2 $70.79   8.129%   $76.5445   $76.54   $76.55   $76.50  
  Purchase #3 $248.36   3.751%   $257.676   $257.68   $257.70   $257.70  
  Purchase #4 $49.75   4.570%   $52.0236   $52.02   $52.00   $52.00  
  Purchase #5 $212.75   4.591%   $222.5174   $222.52   $222.50   $222.50  
  Purchase #6 $177.48   9.871%   $194.9991   $195.00   $195.00   $195.00  
  Purchase #7 $216.48   9.247%   $236.4979   $236.50   $236.50   $236.50  
  7 purchase totals = $1,068.13       $1,143.3332   $1,143.33   $1,143.30   $1,143.30