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 $54.47   3.728%   $56.5006   $56.50   $56.50   $56.50  
  Purchase #2 $33.79   11.410%   $37.6454   $37.65   $37.65   $37.60  
  Purchase #3 $146.45   5.667%   $154.7493   $154.75   $154.75   $154.70  
  Purchase #4 $54.43   5.319%   $57.3251   $57.33   $57.35   $57.30  
  Purchase #5 $226.77   8.435%   $245.898   $245.90   $245.90   $245.90  
  Purchase #6 $182.58   10.728%   $202.1672   $202.17   $202.15   $202.20  
  Purchase #7 $241.82   11.539%   $269.7236   $269.72   $269.70   $269.70  
  7 purchase totals = $940.31       $1,024.0092   $1,024.02   $1,024.00   $1,023.90