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 $199.37   6.795%   $212.9172   $212.92   $212.90   $212.90  
  Purchase #2 $157.76   11.362%   $175.6847   $175.68   $175.70   $175.70  
  Purchase #3 $69.55   7.392%   $74.6911   $74.69   $74.70   $74.70  
  Purchase #4 $179.52   6.845%   $191.8081   $191.81   $191.80   $191.80  
  Purchase #5 $193.29   3.539%   $200.1305   $200.13   $200.15   $200.10  
  Purchase #6 $218.48   11.441%   $243.4763   $243.48   $243.50   $243.50  
  Purchase #7 $151.74   7.468%   $163.0719   $163.07   $163.05   $163.10  
  7 purchase totals = $1,169.71       $1,261.7798   $1,261.78   $1,261.80   $1,261.80