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 $181.72   10.714%   $201.1895   $201.19   $201.20   $201.20  
  Purchase #2 $21.54   12.214%   $24.1709   $24.17   $24.15   $24.20  
  Purchase #3 $148.26   8.379%   $160.6827   $160.68   $160.70   $160.70  
  Purchase #4 $142.71   13.628%   $162.1585   $162.16   $162.15   $162.20  
  Purchase #5 $177.68   10.692%   $196.6775   $196.68   $196.70   $196.70  
  Purchase #6 $66.96   7.483%   $71.9706   $71.97   $71.95   $72.00  
  Purchase #7 $219.51   3.253%   $226.6507   $226.65   $226.65   $226.70  
  7 purchase totals = $958.38       $1,043.5004   $1,043.50   $1,043.50   $1,043.70