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 $65.54   13.770%   $74.5649   $74.56   $74.55   $74.60  
  Purchase #2 $153.85   3.174%   $158.7332   $158.73   $158.75   $158.70  
  Purchase #3 $169.35   3.322%   $174.9758   $174.98   $175.00   $175.00  
  Purchase #4 $86.79   11.365%   $96.6537   $96.65   $96.65   $96.70  
  Purchase #5 $128.28   10.855%   $142.2048   $142.20   $142.20   $142.20  
  Purchase #6 $33.79   4.483%   $35.3048   $35.30   $35.30   $35.30  
  Purchase #7 $29.76   6.360%   $31.6527   $31.65   $31.65   $31.70  
  7 purchase totals = $667.36       $714.0899   $714.07   $714.10   $714.20