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 $64.43   9.726%   $70.6965   $70.70   $70.70   $70.70  
  Purchase #2 $164.43   11.616%   $183.5302   $183.53   $183.55   $183.50  
  Purchase #3 $161.85   8.287%   $175.2625   $175.26   $175.25   $175.30  
  Purchase #4 $192.45   5.626%   $203.2772   $203.28   $203.30   $203.30  
  Purchase #5 $160.53   11.813%   $179.4934   $179.49   $179.50   $179.50  
  Purchase #6 $84.84   11.415%   $94.5245   $94.52   $94.50   $94.50  
  Purchase #7 $98.77   6.739%   $105.4261   $105.43   $105.45   $105.40  
  7 purchase totals = $927.30       $1,012.2104   $1,012.21   $1,012.25   $1,012.20