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 $215.96   10.207%   $238.003   $238.00   $238.00   $238.00  
  Purchase #2 $6.84   3.458%   $7.0765   $7.08   $7.10   $7.10  
  Purchase #3 $47.34   5.634%   $50.0071   $50.01   $50.00   $50.00  
  Purchase #4 $103.32   7.739%   $111.3159   $111.32   $111.30   $111.30  
  Purchase #5 $244.53   12.751%   $275.71   $275.71   $275.70   $275.70  
  Purchase #6 $11.59   3.765%   $12.0264   $12.03   $12.05   $12.00  
  Purchase #7 $192.76   5.565%   $203.4871   $203.49   $203.50   $203.50  
  7 purchase totals = $822.34       $897.6260   $897.64   $897.65   $897.60