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 $64.87   7.360%   $69.6444   $69.64   $69.65   $69.60  
  Purchase #2 $186.62   8.279%   $202.0703   $202.07   $202.05   $202.10  
  Purchase #3 $140.50   4.181%   $146.3743   $146.37   $146.35   $146.40  
  Purchase #4 $219.96   11.618%   $245.515   $245.52   $245.50   $245.50  
  Purchase #5 $82.60   3.216%   $85.2564   $85.26   $85.25   $85.30  
  Purchase #6 $190.90   13.630%   $216.9197   $216.92   $216.90   $216.90  
  Purchase #7 $32.85   7.588%   $35.3427   $35.34   $35.35   $35.30  
  7 purchase totals = $918.30       $1,001.1228   $1,001.12   $1,001.05   $1,001.10