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 $114.93   9.252%   $125.5633   $125.56   $125.55   $125.60  
  Purchase #2 $74.98   3.695%   $77.7505   $77.75   $77.75   $77.80  
  Purchase #3 $118.78   5.783%   $125.649   $125.65   $125.65   $125.60  
  Purchase #4 $27.28   7.793%   $29.4059   $29.41   $29.40   $29.40  
  Purchase #5 $159.58   12.589%   $179.6695   $179.67   $179.65   $179.70  
  Purchase #6 $153.38   12.795%   $173.005   $173.01   $173.00   $173.00  
  Purchase #7 $59.27   6.270%   $62.9862   $62.99   $63.00   $63.00  
  7 purchase totals = $708.20       $774.0294   $774.04   $774.00   $774.10