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 $55.95   12.618%   $63.0098   $63.01   $63.00   $63.00  
  Purchase #2 $220.58   9.865%   $242.3402   $242.34   $242.35   $242.30  
  Purchase #3 $168.80   13.595%   $191.7484   $191.75   $191.75   $191.70  
  Purchase #4 $221.58   8.467%   $240.3412   $240.34   $240.35   $240.30  
  Purchase #5 $227.60   10.523%   $251.5503   $251.55   $251.55   $251.60  
  Purchase #6 $26.34   11.377%   $29.3367   $29.34   $29.35   $29.30  
  Purchase #7 $219.55   5.814%   $232.3146   $232.31   $232.30   $232.30  
  7 purchase totals = $1,140.40       $1,250.6412   $1,250.64   $1,250.65   $1,250.50