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 $207.29   8.273%   $224.4391   $224.44   $224.45   $224.40  
  Purchase #2 $131.66   11.155%   $146.3467   $146.35   $146.35   $146.30  
  Purchase #3 $134.68   13.527%   $152.8982   $152.90   $152.90   $152.90  
  Purchase #4 $49.31   13.539%   $55.9861   $55.99   $56.00   $56.00  
  Purchase #5 $197.25   9.545%   $216.0775   $216.08   $216.10   $216.10  
  Purchase #6 $33.90   4.644%   $35.4743   $35.47   $35.45   $35.50  
  Purchase #7 $84.49   12.392%   $94.96   $94.96   $94.95   $95.00  
  7 purchase totals = $838.58       $926.1819   $926.19   $926.20   $926.20