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 $110.61   13.681%   $125.7426   $125.74   $125.75   $125.70  
  Purchase #2 $68.67   7.740%   $73.9851   $73.99   $74.00   $74.00  
  Purchase #3 $66.46   12.228%   $74.5867   $74.59   $74.60   $74.60  
  Purchase #4 $194.29   4.207%   $202.4638   $202.46   $202.45   $202.50  
  Purchase #5 $36.70   3.713%   $38.0627   $38.06   $38.05   $38.10  
  Purchase #6 $73.81   7.642%   $79.4506   $79.45   $79.45   $79.50  
  Purchase #7 $145.52   4.523%   $152.1019   $152.10   $152.10   $152.10  
  7 purchase totals = $696.06       $746.3934   $746.39   $746.40   $746.50