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 $193.41   13.474%   $219.4701   $219.47   $219.45   $219.50  
  Purchase #2 $234.57   13.677%   $266.6521   $266.65   $266.65   $266.70  
  Purchase #3 $129.28   4.401%   $134.9696   $134.97   $134.95   $135.00  
  Purchase #4 $189.49   13.104%   $214.3208   $214.32   $214.30   $214.30  
  Purchase #5 $149.60   8.162%   $161.8104   $161.81   $161.80   $161.80  
  Purchase #6 $148.43   4.747%   $155.476   $155.48   $155.50   $155.50  
  Purchase #7 $204.26   4.283%   $213.0085   $213.01   $213.00   $213.00  
  7 purchase totals = $1,249.04       $1,365.7075   $1,365.71   $1,365.65   $1,365.80