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 $82.89   6.414%   $88.2066   $88.21   $88.20   $88.20  
  Purchase #2 $25.51   5.754%   $26.9778   $26.98   $27.00   $27.00  
  Purchase #3 $123.48   8.392%   $133.8424   $133.84   $133.85   $133.80  
  Purchase #4 $78.53   5.278%   $82.6748   $82.67   $82.65   $82.70  
  Purchase #5 $7.34   6.355%   $7.8065   $7.81   $7.80   $7.80  
  Purchase #6 $164.45   11.327%   $183.0773   $183.08   $183.10   $183.10  
  Purchase #7 $12.44   6.680%   $13.271   $13.27   $13.25   $13.30  
  7 purchase totals = $494.64       $535.8564   $535.86   $535.85   $535.90