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 $123.48   13.826%   $140.5523   $140.55   $140.55   $140.60  
  Purchase #2 $185.43   9.186%   $202.4636   $202.46   $202.45   $202.50  
  Purchase #3 $67.68   10.226%   $74.601   $74.60   $74.60   $74.60  
  Purchase #4 $247.88   11.604%   $276.644   $276.64   $276.65   $276.60  
  Purchase #5 $165.98   3.593%   $171.9437   $171.94   $171.95   $171.90  
  Purchase #6 $46.81   5.751%   $49.502   $49.50   $49.50   $49.50  
  Purchase #7 $81.41   12.240%   $91.3746   $91.37   $91.35   $91.40  
  7 purchase totals = $918.67       $1,007.0812   $1,007.06   $1,007.05   $1,007.10