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 $204.26   3.862%   $212.1485   $212.15   $212.15   $212.10  
  Purchase #2 $171.50   11.640%   $191.4626   $191.46   $191.45   $191.50  
  Purchase #3 $186.81   13.317%   $211.6875   $211.69   $211.70   $211.70  
  Purchase #4 $82.97   13.416%   $94.1013   $94.10   $94.10   $94.10  
  Purchase #5 $243.87   9.435%   $266.8791   $266.88   $266.90   $266.90  
  Purchase #6 $218.68   13.111%   $247.3511   $247.35   $247.35   $247.40  
  Purchase #7 $119.70   11.236%   $133.1495   $133.15   $133.15   $133.10  
  7 purchase totals = $1,227.79       $1,356.7796   $1,356.78   $1,356.80   $1,356.80