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 $92.61   6.611%   $98.7324   $98.73   $98.75   $98.70  
  Purchase #2 $191.65   12.777%   $216.1371   $216.14   $216.15   $216.10  
  Purchase #3 $249.95   12.829%   $282.0161   $282.02   $282.00   $282.00  
  Purchase #4 $111.95   7.609%   $120.4683   $120.47   $120.45   $120.50  
  Purchase #5 $145.90   6.322%   $155.1238   $155.12   $155.10   $155.10  
  Purchase #6 $142.61   11.563%   $159.1   $159.10   $159.10   $159.10  
  Purchase #7 $189.66   10.193%   $208.992   $208.99   $209.00   $209.00  
  7 purchase totals = $1,124.33       $1,240.5697   $1,240.57   $1,240.55   $1,240.50