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 $67.94   11.533%   $75.7755   $75.78   $75.80   $75.80  
  Purchase #2 $237.25   13.407%   $269.0581   $269.06   $269.05   $269.10  
  Purchase #3 $148.34   11.841%   $165.9049   $165.90   $165.90   $165.90  
  Purchase #4 $120.33   4.792%   $126.0962   $126.10   $126.10   $126.10  
  Purchase #5 $54.91   12.237%   $61.6293   $61.63   $61.65   $61.60  
  Purchase #6 $198.68   10.691%   $219.9209   $219.92   $219.90   $219.90  
  Purchase #7 $68.99   9.629%   $75.633   $75.63   $75.65   $75.60  
  7 purchase totals = $896.44       $994.0179   $994.02   $994.05   $994.00