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 $155.84   3.488%   $161.2757   $161.28   $161.30   $161.30  
  Purchase #2 $24.98   4.860%   $26.194   $26.19   $26.20   $26.20  
  Purchase #3 $54.38   9.702%   $59.6559   $59.66   $59.65   $59.70  
  Purchase #4 $246.90   8.477%   $267.8297   $267.83   $267.85   $267.80  
  Purchase #5 $164.63   10.653%   $182.168   $182.17   $182.15   $182.20  
  Purchase #6 $27.77   4.702%   $29.0757   $29.08   $29.10   $29.10  
  Purchase #7 $156.79   8.289%   $169.7863   $169.79   $169.80   $169.80  
  7 purchase totals = $831.29       $895.9853   $896.00   $896.05   $896.10