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 $68.60   12.182%   $76.9569   $76.96   $76.95   $77.00  
  Purchase #2 $156.26   8.611%   $169.7155   $169.72   $169.70   $169.70  
  Purchase #3 $234.78   12.789%   $264.806   $264.81   $264.80   $264.80  
  Purchase #4 $116.54   13.321%   $132.0643   $132.06   $132.05   $132.10  
  Purchase #5 $76.95   9.361%   $84.1533   $84.15   $84.15   $84.20  
  Purchase #6 $130.41   12.363%   $146.5326   $146.53   $146.55   $146.50  
  Purchase #7 $212.91   7.140%   $228.1118   $228.11   $228.10   $228.10  
  7 purchase totals = $996.45       $1,102.3404   $1,102.34   $1,102.30   $1,102.40