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 $233.69   4.820%   $244.9539   $244.95   $244.95   $245.00  
  Purchase #2 $32.79   10.712%   $36.3025   $36.30   $36.30   $36.30  
  Purchase #3 $86.46   7.154%   $92.6453   $92.65   $92.65   $92.60  
  Purchase #4 $33.85   4.829%   $35.4846   $35.48   $35.50   $35.50  
  Purchase #5 $101.52   12.107%   $113.811   $113.81   $113.80   $113.80  
  Purchase #6 $165.53   10.596%   $183.0696   $183.07   $183.05   $183.10  
  Purchase #7 $36.78   11.658%   $41.0678   $41.07   $41.05   $41.10  
  7 purchase totals = $690.62       $747.3347   $747.33   $747.30   $747.40