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 $213.95   13.721%   $243.3061   $243.31   $243.30   $243.30  
  Purchase #2 $5.97   7.241%   $6.4023   $6.40   $6.40   $6.40  
  Purchase #3 $240.43   4.634%   $251.5715   $251.57   $251.55   $251.60  
  Purchase #4 $62.32   10.694%   $68.9845   $68.98   $69.00   $69.00  
  Purchase #5 $223.94   6.519%   $238.5386   $238.54   $238.55   $238.50  
  Purchase #6 $242.92   8.510%   $263.5925   $263.59   $263.60   $263.60  
  Purchase #7 $69.80   10.777%   $77.3223   $77.32   $77.30   $77.30  
  7 purchase totals = $1,059.33       $1,149.7178   $1,149.71   $1,149.70   $1,149.70