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 $227.72   8.237%   $246.4773   $246.48   $246.50   $246.50  
  Purchase #2 $108.46   5.730%   $114.6748   $114.67   $114.65   $114.70  
  Purchase #3 $75.87   5.535%   $80.0694   $80.07   $80.05   $80.10  
  Purchase #4 $126.80   7.180%   $135.9042   $135.90   $135.90   $135.90  
  Purchase #5 $213.51   4.508%   $223.135   $223.14   $223.15   $223.10  
  Purchase #6 $153.52   13.408%   $174.104   $174.10   $174.10   $174.10  
  Purchase #7 $236.56   8.294%   $256.1803   $256.18   $256.20   $256.20  
  7 purchase totals = $1,142.44       $1,230.5450   $1,230.54   $1,230.55   $1,230.60