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 $60.76   4.802%   $63.6777   $63.68   $63.70   $63.70  
  Purchase #2 $128.69   4.608%   $134.62   $134.62   $134.60   $134.60  
  Purchase #3 $76.35   5.841%   $80.8096   $80.81   $80.80   $80.80  
  Purchase #4 $230.82   4.834%   $241.9778   $241.98   $242.00   $242.00  
  Purchase #5 $97.95   6.715%   $104.5273   $104.53   $104.55   $104.50  
  Purchase #6 $58.72   5.213%   $61.7811   $61.78   $61.80   $61.80  
  Purchase #7 $140.58   4.589%   $147.0312   $147.03   $147.05   $147.00  
  7 purchase totals = $793.87       $834.4247   $834.43   $834.50   $834.40