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 $68.33   9.761%   $74.9997   $75.00   $75.00   $75.00  
  Purchase #2 $6.32   6.202%   $6.712   $6.71   $6.70   $6.70  
  Purchase #3 $249.93   5.451%   $263.5537   $263.55   $263.55   $263.60  
  Purchase #4 $175.38   4.698%   $183.6194   $183.62   $183.60   $183.60  
  Purchase #5 $101.59   3.343%   $104.9862   $104.99   $105.00   $105.00  
  Purchase #6 $58.58   8.107%   $63.3291   $63.33   $63.35   $63.30  
  Purchase #7 $250.95   8.795%   $273.0211   $273.02   $273.00   $273.00  
  7 purchase totals = $911.08       $970.2212   $970.22   $970.20   $970.20