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 $243.37   6.845%   $260.0287   $260.03   $260.05   $260.00  
  Purchase #2 $219.99   11.298%   $244.8445   $244.84   $244.85   $244.80  
  Purchase #3 $126.72   8.859%   $137.9461   $137.95   $137.95   $137.90  
  Purchase #4 $239.27   8.579%   $259.797   $259.80   $259.80   $259.80  
  Purchase #5 $206.34   11.141%   $229.3283   $229.33   $229.35   $229.30  
  Purchase #6 $21.91   4.245%   $22.8401   $22.84   $22.85   $22.80  
  Purchase #7 $60.82   5.778%   $64.3342   $64.33   $64.35   $64.30  
  7 purchase totals = $1,118.42       $1,219.1189   $1,219.12   $1,219.20   $1,218.90