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 $66.98   5.760%   $70.838   $70.84   $70.85   $70.80  
  Purchase #2 $10.63   6.650%   $11.3369   $11.34   $11.35   $11.30  
  Purchase #3 $54.52   7.749%   $58.7448   $58.74   $58.75   $58.70  
  Purchase #4 $245.65   13.844%   $279.6578   $279.66   $279.65   $279.70  
  Purchase #5 $166.40   3.866%   $172.833   $172.83   $172.85   $172.80  
  Purchase #6 $144.60   13.108%   $163.5542   $163.55   $163.55   $163.60  
  Purchase #7 $166.85   7.306%   $179.0401   $179.04   $179.05   $179.00  
  7 purchase totals = $855.63       $936.0048   $936.00   $936.05   $935.90