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 $46.67   11.854%   $52.2023   $52.20   $52.20   $52.20  
  Purchase #2 $195.83   7.787%   $211.0793   $211.08   $211.10   $211.10  
  Purchase #3 $13.63   7.625%   $14.6693   $14.67   $14.65   $14.70  
  Purchase #4 $220.92   10.258%   $243.582   $243.58   $243.60   $243.60  
  Purchase #5 $136.47   8.816%   $148.5012   $148.50   $148.50   $148.50  
  Purchase #6 $134.29   8.635%   $145.8859   $145.89   $145.90   $145.90  
  Purchase #7 $171.38   3.475%   $177.3355   $177.34   $177.35   $177.30  
  7 purchase totals = $919.19       $993.2555   $993.26   $993.30   $993.30