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 $54.92   10.789%   $60.8453   $60.85   $60.85   $60.80  
  Purchase #2 $6.93   6.226%   $7.3615   $7.36   $7.35   $7.40  
  Purchase #3 $95.52   13.620%   $108.5298   $108.53   $108.55   $108.50  
  Purchase #4 $149.44   9.615%   $163.8087   $163.81   $163.80   $163.80  
  Purchase #5 $226.88   13.409%   $257.3023   $257.30   $257.30   $257.30  
  Purchase #6 $100.38   13.273%   $113.7034   $113.70   $113.70   $113.70  
  Purchase #7 $236.82   5.478%   $249.793   $249.79   $249.80   $249.80  
  7 purchase totals = $870.89       $961.3440   $961.34   $961.35   $961.30