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 $56.51   11.424%   $62.9657   $62.97   $62.95   $63.00  
  Purchase #2 $241.79   6.624%   $257.8062   $257.81   $257.80   $257.80  
  Purchase #3 $228.71   8.618%   $248.4202   $248.42   $248.40   $248.40  
  Purchase #4 $201.84   9.472%   $220.9583   $220.96   $220.95   $221.00  
  Purchase #5 $43.89   12.318%   $49.2964   $49.30   $49.30   $49.30  
  Purchase #6 $76.75   8.784%   $83.4917   $83.49   $83.50   $83.50  
  Purchase #7 $145.49   13.749%   $165.4934   $165.49   $165.50   $165.50  
  7 purchase totals = $994.98       $1,088.4319   $1,088.44   $1,088.40   $1,088.50