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 $39.68   10.803%   $43.9666   $43.97   $43.95   $44.00  
  Purchase #2 $165.33   7.294%   $177.3892   $177.39   $177.40   $177.40  
  Purchase #3 $192.56   7.352%   $206.717   $206.72   $206.70   $206.70  
  Purchase #4 $33.61   11.111%   $37.3444   $37.34   $37.35   $37.30  
  Purchase #5 $249.65   13.684%   $283.8121   $283.81   $283.80   $283.80  
  Purchase #6 $91.66   11.127%   $101.859   $101.86   $101.85   $101.90  
  Purchase #7 $213.45   12.836%   $240.8484   $240.85   $240.85   $240.80  
  7 purchase totals = $985.94       $1,091.9367   $1,091.94   $1,091.90   $1,091.90