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 $92.52   5.268%   $97.394   $97.39   $97.40   $97.40  
  Purchase #2 $126.55   10.326%   $139.6176   $139.62   $139.60   $139.60  
  Purchase #3 $239.31   9.582%   $262.2407   $262.24   $262.25   $262.20  
  Purchase #4 $203.79   11.476%   $227.1769   $227.18   $227.20   $227.20  
  Purchase #5 $157.36   13.846%   $179.1481   $179.15   $179.15   $179.10  
  Purchase #6 $126.76   9.358%   $138.6222   $138.62   $138.60   $138.60  
  Purchase #7 $202.79   11.833%   $226.7861   $226.79   $226.80   $226.80  
  7 purchase totals = $1,149.08       $1,270.9856   $1,270.99   $1,271.00   $1,270.90