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 $208.80   9.322%   $228.2643   $228.26   $228.25   $228.30  
  Purchase #2 $161.40   4.696%   $168.9793   $168.98   $169.00   $169.00  
  Purchase #3 $113.64   10.284%   $125.3267   $125.33   $125.35   $125.30  
  Purchase #4 $120.55   5.113%   $126.7137   $126.71   $126.70   $126.70  
  Purchase #5 $211.98   7.554%   $227.993   $227.99   $228.00   $228.00  
  Purchase #6 $34.31   8.598%   $37.26   $37.26   $37.25   $37.30  
  Purchase #7 $50.79   8.569%   $55.1422   $55.14   $55.15   $55.10  
  7 purchase totals = $901.47       $969.6792   $969.67   $969.70   $969.70