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 $148.25   12.545%   $166.848   $166.85   $166.85   $166.80  
  Purchase #2 $211.58   5.654%   $223.5427   $223.54   $223.55   $223.50  
  Purchase #3 $113.94   9.419%   $124.672   $124.67   $124.65   $124.70  
  Purchase #4 $156.66   3.414%   $162.0084   $162.01   $162.00   $162.00  
  Purchase #5 $66.76   6.318%   $70.9779   $70.98   $71.00   $71.00  
  Purchase #6 $45.58   5.669%   $48.1639   $48.16   $48.15   $48.20  
  Purchase #7 $187.69   9.132%   $204.8299   $204.83   $204.85   $204.80  
  7 purchase totals = $930.46       $1,001.0428   $1,001.04   $1,001.05   $1,001.00