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 $135.70   13.467%   $153.9747   $153.97   $153.95   $154.00  
  Purchase #2 $206.36   6.414%   $219.5959   $219.60   $219.60   $219.60  
  Purchase #3 $189.69   4.549%   $198.319   $198.32   $198.30   $198.30  
  Purchase #4 $220.84   5.233%   $232.3966   $232.40   $232.40   $232.40  
  Purchase #5 $151.99   9.156%   $165.9062   $165.91   $165.90   $165.90  
  Purchase #6 $190.29   6.129%   $201.9529   $201.95   $201.95   $202.00  
  Purchase #7 $31.31   7.363%   $33.6154   $33.62   $33.60   $33.60  
  7 purchase totals = $1,126.18       $1,205.7607   $1,205.77   $1,205.70   $1,205.80