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 $168.67   9.322%   $184.3934   $184.39   $184.40   $184.40  
  Purchase #2 $50.57   12.178%   $56.7284   $56.73   $56.75   $56.70  
  Purchase #3 $60.59   11.408%   $67.5021   $67.50   $67.50   $67.50  
  Purchase #4 $178.40   5.756%   $188.6687   $188.67   $188.65   $188.70  
  Purchase #5 $44.70   9.232%   $48.8267   $48.83   $48.85   $48.80  
  Purchase #6 $246.94   8.512%   $267.9595   $267.96   $267.95   $268.00  
  Purchase #7 $213.99   11.629%   $238.8749   $238.87   $238.85   $238.90  
  7 purchase totals = $963.86       $1,052.9537   $1,052.95   $1,052.95   $1,053.00