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 $65.84   12.122%   $73.8211   $73.82   $73.80   $73.80  
  Purchase #2 $82.35   4.482%   $86.0409   $86.04   $86.05   $86.00  
  Purchase #3 $207.86   11.667%   $232.111   $232.11   $232.10   $232.10  
  Purchase #4 $73.90   3.801%   $76.7089   $76.71   $76.70   $76.70  
  Purchase #5 $169.79   8.831%   $184.7842   $184.78   $184.80   $184.80  
  Purchase #6 $184.67   4.608%   $193.1796   $193.18   $193.20   $193.20  
  Purchase #7 $35.96   8.516%   $39.0224   $39.02   $39.00   $39.00  
  7 purchase totals = $820.37       $885.6681   $885.66   $885.65   $885.60