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 $41.43   5.286%   $43.62   $43.62   $43.60   $43.60  
  Purchase #2 $247.31   12.455%   $278.1125   $278.11   $278.10   $278.10  
  Purchase #3 $181.33   6.831%   $193.7167   $193.72   $193.70   $193.70  
  Purchase #4 $174.59   11.701%   $195.0188   $195.02   $195.00   $195.00  
  Purchase #5 $40.53   7.319%   $43.4964   $43.50   $43.50   $43.50  
  Purchase #6 $47.64   3.301%   $49.2126   $49.21   $49.20   $49.20  
  Purchase #7 $207.50   5.216%   $218.3232   $218.32   $218.30   $218.30  
  7 purchase totals = $940.33       $1,021.5002   $1,021.50   $1,021.40   $1,021.40