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 $200.96   8.853%   $218.751   $218.75   $218.75   $218.80  
  Purchase #2 $221.49   3.818%   $229.9465   $229.95   $229.95   $229.90  
  Purchase #3 $178.45   8.446%   $193.5219   $193.52   $193.50   $193.50  
  Purchase #4 $56.75   8.543%   $61.5982   $61.60   $61.60   $61.60  
  Purchase #5 $126.28   7.348%   $135.5591   $135.56   $135.55   $135.60  
  Purchase #6 $113.97   10.526%   $125.9665   $125.97   $125.95   $126.00  
  Purchase #7 $96.51   10.569%   $106.7101   $106.71   $106.70   $106.70  
  7 purchase totals = $994.41       $1,072.0533   $1,072.06   $1,072.00   $1,072.10