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 $20.33   10.200%   $22.4037   $22.40   $22.40   $22.40  
  Purchase #2 $187.72   5.520%   $198.0821   $198.08   $198.10   $198.10  
  Purchase #3 $31.98   9.637%   $35.0619   $35.06   $35.05   $35.10  
  Purchase #4 $112.50   4.516%   $117.5805   $117.58   $117.60   $117.60  
  Purchase #5 $51.39   3.115%   $52.9908   $52.99   $53.00   $53.00  
  Purchase #6 $152.86   11.732%   $170.7935   $170.79   $170.80   $170.80  
  Purchase #7 $68.34   6.376%   $72.6974   $72.70   $72.70   $72.70  
  7 purchase totals = $625.12       $669.6099   $669.60   $669.65   $669.70