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 $66.37   12.752%   $74.8335   $74.83   $74.85   $74.80  
  Purchase #2 $238.25   5.376%   $251.0583   $251.06   $251.05   $251.10  
  Purchase #3 $105.86   6.416%   $112.652   $112.65   $112.65   $112.70  
  Purchase #4 $245.39   4.200%   $255.6964   $255.70   $255.70   $255.70  
  Purchase #5 $85.98   3.274%   $88.795   $88.80   $88.80   $88.80  
  Purchase #6 $73.49   4.134%   $76.5281   $76.53   $76.55   $76.50  
  Purchase #7 $181.39   7.169%   $194.3938   $194.39   $194.40   $194.40  
  7 purchase totals = $996.73       $1,053.9571   $1,053.96   $1,054.00   $1,054.00