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 $61.73   10.482%   $68.2005   $68.20   $68.20   $68.20  
  Purchase #2 $87.47   10.700%   $96.8293   $96.83   $96.85   $96.80  
  Purchase #3 $235.26   3.136%   $242.6378   $242.64   $242.65   $242.60  
  Purchase #4 $209.62   10.772%   $232.2003   $232.20   $232.20   $232.20  
  Purchase #5 $232.47   3.494%   $240.5925   $240.59   $240.60   $240.60  
  Purchase #6 $238.36   4.751%   $249.6845   $249.68   $249.70   $249.70  
  Purchase #7 $193.98   4.153%   $202.036   $202.04   $202.05   $202.00  
  7 purchase totals = $1,258.89       $1,332.1809   $1,332.18   $1,332.25   $1,332.10