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 $53.96   12.734%   $60.8313   $60.83   $60.85   $60.80  
  Purchase #2 $29.95   8.131%   $32.3852   $32.39   $32.40   $32.40  
  Purchase #3 $237.48   9.556%   $260.1736   $260.17   $260.15   $260.20  
  Purchase #4 $50.60   11.744%   $56.5425   $56.54   $56.55   $56.50  
  Purchase #5 $231.40   13.645%   $262.9745   $262.97   $262.95   $263.00  
  Purchase #6 $210.52   7.658%   $226.6416   $226.64   $226.65   $226.60  
  Purchase #7 $59.45   10.462%   $65.6697   $65.67   $65.65   $65.70  
  7 purchase totals = $873.36       $965.2184   $965.21   $965.20   $965.20