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 $79.86   6.369%   $84.9463   $84.95   $84.95   $84.90  
  Purchase #2 $154.37   7.265%   $165.585   $165.59   $165.60   $165.60  
  Purchase #3 $193.95   4.385%   $202.4547   $202.45   $202.45   $202.50  
  Purchase #4 $199.90   12.411%   $224.7096   $224.71   $224.70   $224.70  
  Purchase #5 $74.46   6.618%   $79.3878   $79.39   $79.40   $79.40  
  Purchase #6 $93.56   7.598%   $100.6687   $100.67   $100.65   $100.70  
  Purchase #7 $178.33   11.223%   $198.344   $198.34   $198.35   $198.30  
  7 purchase totals = $974.43       $1,056.0961   $1,056.10   $1,056.10   $1,056.10