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 $146.65   12.661%   $165.2174   $165.22   $165.20   $165.20  
  Purchase #2 $171.37   8.832%   $186.5054   $186.51   $186.50   $186.50  
  Purchase #3 $51.94   12.602%   $58.4855   $58.49   $58.50   $58.50  
  Purchase #4 $229.72   11.164%   $255.3659   $255.37   $255.35   $255.40  
  Purchase #5 $138.64   4.604%   $145.023   $145.02   $145.00   $145.00  
  Purchase #6 $13.98   6.319%   $14.8634   $14.86   $14.85   $14.90  
  Purchase #7 $182.60   10.515%   $201.8004   $201.80   $201.80   $201.80  
  7 purchase totals = $934.90       $1,027.2610   $1,027.27   $1,027.20   $1,027.30