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 $211.34   5.868%   $223.7414   $223.74   $223.75   $223.70  
  Purchase #2 $183.64   11.735%   $205.1902   $205.19   $205.20   $205.20  
  Purchase #3 $126.97   9.264%   $138.7325   $138.73   $138.75   $138.70  
  Purchase #4 $17.25   6.381%   $18.3507   $18.35   $18.35   $18.40  
  Purchase #5 $56.61   12.293%   $63.5691   $63.57   $63.55   $63.60  
  Purchase #6 $248.95   13.300%   $282.0604   $282.06   $282.05   $282.10  
  Purchase #7 $52.46   13.698%   $59.646   $59.65   $59.65   $59.60  
  7 purchase totals = $897.22       $991.2903   $991.29   $991.30   $991.30