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 $35.32   6.675%   $37.6776   $37.68   $37.70   $37.70  
  Purchase #2 $88.47   8.359%   $95.8652   $95.87   $95.85   $95.90  
  Purchase #3 $186.54   3.357%   $192.8021   $192.80   $192.80   $192.80  
  Purchase #4 $141.64   12.605%   $159.4937   $159.49   $159.50   $159.50  
  Purchase #5 $89.36   6.793%   $95.4302   $95.43   $95.45   $95.40  
  Purchase #6 $120.92   7.415%   $129.8862   $129.89   $129.90   $129.90  
  Purchase #7 $88.33   7.815%   $95.233   $95.23   $95.25   $95.20  
  7 purchase totals = $750.58       $806.3880   $806.39   $806.45   $806.40