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 $222.67   10.852%   $246.8341   $246.83   $246.85   $246.80  
  Purchase #2 $241.92   7.697%   $260.5406   $260.54   $260.55   $260.50  
  Purchase #3 $19.46   10.378%   $21.4796   $21.48   $21.50   $21.50  
  Purchase #4 $67.52   10.584%   $74.6663   $74.67   $74.65   $74.70  
  Purchase #5 $247.59   8.850%   $269.5017   $269.50   $269.50   $269.50  
  Purchase #6 $90.96   12.842%   $102.6411   $102.64   $102.65   $102.60  
  Purchase #7 $163.26   13.283%   $184.9458   $184.95   $184.95   $184.90  
  7 purchase totals = $1,053.38       $1,160.6092   $1,160.61   $1,160.65   $1,160.50