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 $241.96   13.848%   $275.4666   $275.47   $275.45   $275.50  
  Purchase #2 $111.80   9.405%   $122.3148   $122.31   $122.30   $122.30  
  Purchase #3 $43.66   11.813%   $48.8176   $48.82   $48.80   $48.80  
  Purchase #4 $57.83   5.872%   $61.2258   $61.23   $61.25   $61.20  
  Purchase #5 $239.87   7.141%   $256.9991   $257.00   $257.00   $257.00  
  Purchase #6 $105.74   4.187%   $110.1673   $110.17   $110.15   $110.20  
  Purchase #7 $179.27   9.475%   $196.2558   $196.26   $196.25   $196.30  
  7 purchase totals = $980.13       $1,071.2470   $1,071.26   $1,071.20   $1,071.30