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 $206.54   12.806%   $232.9895   $232.99   $233.00   $233.00  
  Purchase #2 $62.80   10.424%   $69.3463   $69.35   $69.35   $69.30  
  Purchase #3 $179.79   7.825%   $193.8586   $193.86   $193.85   $193.90  
  Purchase #4 $149.28   10.598%   $165.1007   $165.10   $165.10   $165.10  
  Purchase #5 $221.62   12.834%   $250.0627   $250.06   $250.05   $250.10  
  Purchase #6 $124.73   6.241%   $132.5144   $132.51   $132.50   $132.50  
  Purchase #7 $225.84   11.265%   $251.2809   $251.28   $251.30   $251.30  
  7 purchase totals = $1,170.60       $1,295.1531   $1,295.15   $1,295.15   $1,295.20