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 $148.49   8.393%   $160.9528   $160.95   $160.95   $161.00  
  Purchase #2 $140.45   11.147%   $156.106   $156.11   $156.10   $156.10  
  Purchase #3 $72.28   9.611%   $79.2268   $79.23   $79.25   $79.20  
  Purchase #4 $212.85   4.451%   $222.324   $222.32   $222.30   $222.30  
  Purchase #5 $139.66   7.828%   $150.5926   $150.59   $150.60   $150.60  
  Purchase #6 $210.25   11.385%   $234.187   $234.19   $234.20   $234.20  
  Purchase #7 $56.86   7.747%   $61.2649   $61.26   $61.25   $61.30  
  7 purchase totals = $980.84       $1,064.6541   $1,064.65   $1,064.65   $1,064.70