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 $61.92   8.745%   $67.3349   $67.33   $67.35   $67.30  
  Purchase #2 $164.29   5.280%   $172.9645   $172.96   $172.95   $173.00  
  Purchase #3 $140.25   11.653%   $156.5933   $156.59   $156.60   $156.60  
  Purchase #4 $88.88   4.692%   $93.0502   $93.05   $93.05   $93.10  
  Purchase #5 $230.98   3.767%   $239.681   $239.68   $239.70   $239.70  
  Purchase #6 $131.25   13.334%   $148.7509   $148.75   $148.75   $148.80  
  Purchase #7 $62.68   12.258%   $70.3633   $70.36   $70.35   $70.40  
  7 purchase totals = $880.25       $948.7381   $948.72   $948.75   $948.90