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 $180.37   9.610%   $197.7036   $197.70   $197.70   $197.70  
  Purchase #2 $238.96   11.670%   $266.8466   $266.85   $266.85   $266.80  
  Purchase #3 $147.37   9.501%   $161.3716   $161.37   $161.35   $161.40  
  Purchase #4 $211.83   9.309%   $231.5493   $231.55   $231.55   $231.50  
  Purchase #5 $173.77   11.629%   $193.9777   $193.98   $194.00   $194.00  
  Purchase #6 $250.92   4.641%   $262.5652   $262.57   $262.55   $262.60  
  Purchase #7 $83.59   11.269%   $93.0098   $93.01   $93.00   $93.00  
  7 purchase totals = $1,286.81       $1,407.0238   $1,407.03   $1,407.00   $1,407.00