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 $74.89   12.215%   $84.0378   $84.04   $84.05   $84.00  
  Purchase #2 $195.99   7.433%   $210.5579   $210.56   $210.55   $210.60  
  Purchase #3 $122.98   7.417%   $132.1014   $132.10   $132.10   $132.10  
  Purchase #4 $152.73   9.271%   $166.8896   $166.89   $166.90   $166.90  
  Purchase #5 $110.28   9.413%   $120.6607   $120.66   $120.65   $120.70  
  Purchase #6 $190.31   4.628%   $199.1175   $199.12   $199.10   $199.10  
  Purchase #7 $85.88   7.554%   $92.3674   $92.37   $92.35   $92.40  
  7 purchase totals = $933.06       $1,005.7323   $1,005.74   $1,005.70   $1,005.80