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 $247.61   7.345%   $265.797   $265.80   $265.80   $265.80  
  Purchase #2 $74.78   9.198%   $81.6583   $81.66   $81.65   $81.70  
  Purchase #3 $97.91   3.718%   $101.5503   $101.55   $101.55   $101.60  
  Purchase #4 $77.93   7.764%   $83.9805   $83.98   $84.00   $84.00  
  Purchase #5 $208.92   7.544%   $224.6809   $224.68   $224.70   $224.70  
  Purchase #6 $55.93   10.805%   $61.9732   $61.97   $61.95   $62.00  
  Purchase #7 $209.60   13.695%   $238.3047   $238.30   $238.30   $238.30  
  7 purchase totals = $972.68       $1,057.9449   $1,057.94   $1,057.95   $1,058.10