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 $48.82   9.689%   $53.5502   $53.55   $53.55   $53.60  
  Purchase #2 $60.43   5.498%   $63.7524   $63.75   $63.75   $63.80  
  Purchase #3 $145.93   3.350%   $150.8187   $150.82   $150.80   $150.80  
  Purchase #4 $35.48   7.447%   $38.1222   $38.12   $38.10   $38.10  
  Purchase #5 $105.64   11.365%   $117.646   $117.65   $117.65   $117.60  
  Purchase #6 $249.55   7.617%   $268.5582   $268.56   $268.55   $268.60  
  Purchase #7 $176.57   3.758%   $183.2055   $183.21   $183.20   $183.20  
  7 purchase totals = $822.42       $875.6532   $875.66   $875.60   $875.70