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 $172.80   6.550%   $184.1184   $184.12   $184.10   $184.10  
  Purchase #2 $246.61   4.305%   $257.2266   $257.23   $257.25   $257.20  
  Purchase #3 $11.67   11.531%   $13.0157   $13.02   $13.00   $13.00  
  Purchase #4 $156.64   5.655%   $165.498   $165.50   $165.50   $165.50  
  Purchase #5 $234.97   12.641%   $264.6726   $264.67   $264.65   $264.70  
  Purchase #6 $226.93   3.773%   $235.4921   $235.49   $235.50   $235.50  
  Purchase #7 $232.62   4.121%   $242.2063   $242.21   $242.20   $242.20  
  7 purchase totals = $1,282.24       $1,362.2297   $1,362.24   $1,362.20   $1,362.20