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 $145.77   13.219%   $165.0393   $165.04   $165.05   $165.00  
  Purchase #2 $41.62   10.217%   $45.8723   $45.87   $45.85   $45.90  
  Purchase #3 $73.90   3.850%   $76.7452   $76.75   $76.75   $76.70  
  Purchase #4 $250.65   5.844%   $265.298   $265.30   $265.30   $265.30  
  Purchase #5 $191.61   5.473%   $202.0968   $202.10   $202.10   $202.10  
  Purchase #6 $55.56   13.367%   $62.9867   $62.99   $63.00   $63.00  
  Purchase #7 $5.52   3.686%   $5.7235   $5.72   $5.70   $5.70  
  7 purchase totals = $764.63       $823.7618   $823.77   $823.75   $823.70