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 $170.81   7.523%   $183.66   $183.66   $183.65   $183.70  
  Purchase #2 $22.55   9.470%   $24.6855   $24.69   $24.70   $24.70  
  Purchase #3 $48.93   11.435%   $54.5251   $54.53   $54.55   $54.50  
  Purchase #4 $49.46   8.170%   $53.5009   $53.50   $53.50   $53.50  
  Purchase #5 $189.89   7.362%   $203.8697   $203.87   $203.85   $203.90  
  Purchase #6 $66.49   11.722%   $74.284   $74.28   $74.30   $74.30  
  Purchase #7 $215.48   9.167%   $235.2331   $235.23   $235.25   $235.20  
  7 purchase totals = $763.61       $829.7583   $829.76   $829.80   $829.80