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 $84.51   9.210%   $92.2934   $92.29   $92.30   $92.30  
  Purchase #2 $178.50   12.393%   $200.6215   $200.62   $200.60   $200.60  
  Purchase #3 $105.51   11.553%   $117.6996   $117.70   $117.70   $117.70  
  Purchase #4 $195.94   9.587%   $214.7248   $214.72   $214.70   $214.70  
  Purchase #5 $201.73   8.173%   $218.2174   $218.22   $218.20   $218.20  
  Purchase #6 $216.67   13.448%   $245.8078   $245.81   $245.80   $245.80  
  Purchase #7 $219.77   4.205%   $229.0113   $229.01   $229.00   $229.00  
  7 purchase totals = $1,202.63       $1,318.3758   $1,318.37   $1,318.30   $1,318.30