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 $69.75   10.709%   $77.2195   $77.22   $77.20   $77.20  
  Purchase #2 $145.83   5.613%   $154.0154   $154.02   $154.00   $154.00  
  Purchase #3 $215.46   4.392%   $224.923   $224.92   $224.90   $224.90  
  Purchase #4 $153.48   8.120%   $165.9426   $165.94   $165.95   $165.90  
  Purchase #5 $207.76   11.870%   $232.4211   $232.42   $232.40   $232.40  
  Purchase #6 $21.27   13.850%   $24.2159   $24.22   $24.20   $24.20  
  Purchase #7 $171.89   5.454%   $181.2649   $181.26   $181.25   $181.30  
  7 purchase totals = $985.44       $1,060.0024   $1,060.00   $1,059.90   $1,059.90