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 $149.55   8.110%   $161.6785   $161.68   $161.70   $161.70  
  Purchase #2 $184.42   13.235%   $208.828   $208.83   $208.85   $208.80  
  Purchase #3 $33.31   11.227%   $37.0497   $37.05   $37.05   $37.00  
  Purchase #4 $57.59   6.523%   $61.3466   $61.35   $61.35   $61.30  
  Purchase #5 $121.64   8.220%   $131.6388   $131.64   $131.65   $131.60  
  Purchase #6 $229.51   7.446%   $246.5993   $246.60   $246.60   $246.60  
  Purchase #7 $150.75   12.490%   $169.5787   $169.58   $169.60   $169.60  
  7 purchase totals = $926.77       $1,016.7196   $1,016.73   $1,016.80   $1,016.60