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 $207.73   5.484%   $219.1219   $219.12   $219.10   $219.10  
  Purchase #2 $221.37   9.421%   $242.2253   $242.23   $242.25   $242.20  
  Purchase #3 $30.86   13.861%   $35.1375   $35.14   $35.15   $35.10  
  Purchase #4 $165.84   6.813%   $177.1387   $177.14   $177.15   $177.10  
  Purchase #5 $175.52   9.665%   $192.484   $192.48   $192.50   $192.50  
  Purchase #6 $32.34   11.232%   $35.9724   $35.97   $35.95   $36.00  
  Purchase #7 $169.67   12.318%   $190.57   $190.57   $190.55   $190.60  
  7 purchase totals = $1,003.33       $1,092.6498   $1,092.65   $1,092.65   $1,092.60