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 $136.34   12.726%   $153.6906   $153.69   $153.70   $153.70  
  Purchase #2 $53.49   5.356%   $56.3549   $56.35   $56.35   $56.40  
  Purchase #3 $11.71   4.680%   $12.258   $12.26   $12.25   $12.30  
  Purchase #4 $216.36   12.319%   $243.0134   $243.01   $243.00   $243.00  
  Purchase #5 $181.51   9.697%   $199.111   $199.11   $199.10   $199.10  
  Purchase #6 $206.91   6.270%   $219.8833   $219.88   $219.90   $219.90  
  Purchase #7 $170.44   5.116%   $179.1597   $179.16   $179.15   $179.20  
  7 purchase totals = $976.76       $1,063.4709   $1,063.46   $1,063.45   $1,063.60