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 $243.50   12.540%   $274.0349   $274.03   $274.05   $274.00  
  Purchase #2 $49.27   9.539%   $53.9699   $53.97   $53.95   $54.00  
  Purchase #3 $75.69   13.828%   $86.1564   $86.16   $86.15   $86.20  
  Purchase #4 $139.54   8.158%   $150.9237   $150.92   $150.90   $150.90  
  Purchase #5 $51.30   7.276%   $55.0326   $55.03   $55.05   $55.00  
  Purchase #6 $215.30   6.822%   $229.9878   $229.99   $230.00   $230.00  
  Purchase #7 $224.35   12.575%   $252.562   $252.56   $252.55   $252.60  
  7 purchase totals = $998.95       $1,102.6673   $1,102.66   $1,102.65   $1,102.70