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 $122.34   12.505%   $137.6386   $137.64   $137.65   $137.60  
  Purchase #2 $159.97   7.203%   $171.4926   $171.49   $171.50   $171.50  
  Purchase #3 $9.75   3.414%   $10.0829   $10.08   $10.10   $10.10  
  Purchase #4 $84.94   13.125%   $96.0884   $96.09   $96.10   $96.10  
  Purchase #5 $179.55   12.270%   $201.5808   $201.58   $201.60   $201.60  
  Purchase #6 $84.35   11.715%   $94.2316   $94.23   $94.25   $94.20  
  Purchase #7 $44.28   3.522%   $45.8395   $45.84   $45.85   $45.80  
  7 purchase totals = $685.18       $756.9544   $756.95   $757.05   $756.90