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 $154.91   7.816%   $167.0178   $167.02   $167.00   $167.00  
  Purchase #2 $227.94   13.827%   $259.4573   $259.46   $259.45   $259.50  
  Purchase #3 $162.70   10.173%   $179.2515   $179.25   $179.25   $179.30  
  Purchase #4 $242.79   3.709%   $251.7951   $251.80   $251.80   $251.80  
  Purchase #5 $62.59   12.855%   $70.6359   $70.64   $70.65   $70.60  
  Purchase #6 $25.77   7.118%   $27.6043   $27.60   $27.60   $27.60  
  Purchase #7 $37.26   3.129%   $38.4259   $38.43   $38.45   $38.40  
  7 purchase totals = $913.96       $994.1878   $994.20   $994.20   $994.20