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 $211.99   12.247%   $237.9524   $237.95   $237.95   $238.00  
  Purchase #2 $74.52   9.182%   $81.3624   $81.36   $81.35   $81.40  
  Purchase #3 $21.36   6.745%   $22.8007   $22.80   $22.80   $22.80  
  Purchase #4 $31.42   7.568%   $33.7979   $33.80   $33.80   $33.80  
  Purchase #5 $11.31   8.695%   $12.2934   $12.29   $12.30   $12.30  
  Purchase #6 $151.86   5.714%   $160.5373   $160.54   $160.55   $160.50  
  Purchase #7 $225.86   9.716%   $247.8046   $247.80   $247.80   $247.80  
  7 purchase totals = $728.32       $796.5487   $796.54   $796.55   $796.60