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 $166.49   6.738%   $177.7081   $177.71   $177.70   $177.70  
  Purchase #2 $185.90   6.431%   $197.8552   $197.86   $197.85   $197.90  
  Purchase #3 $21.85   9.815%   $23.9946   $23.99   $24.00   $24.00  
  Purchase #4 $40.61   7.288%   $43.5697   $43.57   $43.55   $43.60  
  Purchase #5 $62.62   13.248%   $70.9159   $70.92   $70.90   $70.90  
  Purchase #6 $243.35   12.798%   $274.4939   $274.49   $274.50   $274.50  
  Purchase #7 $211.42   11.296%   $235.302   $235.30   $235.30   $235.30  
  7 purchase totals = $932.24       $1,023.8394   $1,023.84   $1,023.80   $1,023.90