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 $95.78   6.348%   $101.8601   $101.86   $101.85   $101.90  
  Purchase #2 $159.75   9.772%   $175.3608   $175.36   $175.35   $175.40  
  Purchase #3 $53.86   10.423%   $59.4738   $59.47   $59.45   $59.50  
  Purchase #4 $213.56   5.821%   $225.9913   $225.99   $226.00   $226.00  
  Purchase #5 $108.57   12.274%   $121.8959   $121.90   $121.90   $121.90  
  Purchase #6 $22.98   7.266%   $24.6497   $24.65   $24.65   $24.60  
  Purchase #7 $219.68   6.285%   $233.4869   $233.49   $233.50   $233.50  
  7 purchase totals = $874.18       $942.7185   $942.72   $942.70   $942.80