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 $61.46   10.131%   $67.6865   $67.69   $67.70   $67.70  
  Purchase #2 $156.89   7.250%   $168.2645   $168.26   $168.25   $168.30  
  Purchase #3 $172.43   12.712%   $194.3493   $194.35   $194.35   $194.30  
  Purchase #4 $170.43   13.262%   $193.0324   $193.03   $193.05   $193.00  
  Purchase #5 $200.29   10.125%   $220.5694   $220.57   $220.55   $220.60  
  Purchase #6 $217.40   7.834%   $234.4311   $234.43   $234.45   $234.40  
  Purchase #7 $158.70   9.172%   $173.256   $173.26   $173.25   $173.30  
  7 purchase totals = $1,137.60       $1,251.5892   $1,251.59   $1,251.60   $1,251.60