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 $56.51   9.524%   $61.892   $61.89   $61.90   $61.90  
  Purchase #2 $58.80   3.179%   $60.6693   $60.67   $60.65   $60.70  
  Purchase #3 $155.64   6.241%   $165.3535   $165.35   $165.35   $165.40  
  Purchase #4 $221.94   11.103%   $246.582   $246.58   $246.60   $246.60  
  Purchase #5 $124.66   7.710%   $134.2713   $134.27   $134.25   $134.30  
  Purchase #6 $117.98   13.363%   $133.7457   $133.75   $133.75   $133.70  
  Purchase #7 $193.28   8.720%   $210.134   $210.13   $210.15   $210.10  
  7 purchase totals = $928.81       $1,012.6478   $1,012.64   $1,012.65   $1,012.70