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 $232.91   12.547%   $262.1332   $262.13   $262.15   $262.10  
  Purchase #2 $56.35   5.704%   $59.5642   $59.56   $59.55   $59.60  
  Purchase #3 $129.32   3.748%   $134.1669   $134.17   $134.15   $134.20  
  Purchase #4 $235.49   4.475%   $246.0282   $246.03   $246.05   $246.00  
  Purchase #5 $150.28   10.873%   $166.6199   $166.62   $166.60   $166.60  
  Purchase #6 $11.53   5.680%   $12.1849   $12.18   $12.20   $12.20  
  Purchase #7 $169.62   5.541%   $179.0186   $179.02   $179.00   $179.00  
  7 purchase totals = $985.50       $1,059.7159   $1,059.71   $1,059.70   $1,059.70