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 $71.92   6.377%   $76.5063   $76.51   $76.50   $76.50  
  Purchase #2 $41.58   10.770%   $46.0582   $46.06   $46.05   $46.10  
  Purchase #3 $219.96   10.268%   $242.5455   $242.55   $242.55   $242.50  
  Purchase #4 $63.36   6.305%   $67.3548   $67.35   $67.35   $67.40  
  Purchase #5 $77.67   3.182%   $80.1415   $80.14   $80.15   $80.10  
  Purchase #6 $211.92   5.603%   $223.7939   $223.79   $223.80   $223.80  
  Purchase #7 $205.36   12.313%   $230.646   $230.65   $230.65   $230.60  
  7 purchase totals = $891.77       $967.0462   $967.05   $967.05   $967.00