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 $56.35   6.782%   $60.1717   $60.17   $60.15   $60.20  
  Purchase #2 $82.62   11.787%   $92.3584   $92.36   $92.35   $92.40  
  Purchase #3 $76.52   11.580%   $85.381   $85.38   $85.40   $85.40  
  Purchase #4 $230.74   9.252%   $252.0881   $252.09   $252.10   $252.10  
  Purchase #5 $198.56   6.514%   $211.4942   $211.49   $211.50   $211.50  
  Purchase #6 $121.33   10.307%   $133.8355   $133.84   $133.85   $133.80  
  Purchase #7 $17.37   7.702%   $18.7078   $18.71   $18.70   $18.70  
  7 purchase totals = $783.49       $854.0367   $854.04   $854.05   $854.10