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 $83.27   12.311%   $93.5214   $93.52   $93.50   $93.50  
  Purchase #2 $61.67   3.213%   $63.6515   $63.65   $63.65   $63.70  
  Purchase #3 $9.81   7.183%   $10.5147   $10.51   $10.50   $10.50  
  Purchase #4 $246.42   7.231%   $264.2386   $264.24   $264.25   $264.20  
  Purchase #5 $237.63   13.271%   $269.1659   $269.17   $269.15   $269.20  
  Purchase #6 $172.58   7.108%   $184.847   $184.85   $184.85   $184.80  
  Purchase #7 $120.70   9.669%   $132.3705   $132.37   $132.35   $132.40  
  7 purchase totals = $932.08       $1,018.3096   $1,018.31   $1,018.25   $1,018.30