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 $211.86   5.397%   $223.2941   $223.29   $223.30   $223.30  
  Purchase #2 $216.68   13.319%   $245.5396   $245.54   $245.55   $245.50  
  Purchase #3 $199.60   6.656%   $212.8854   $212.89   $212.90   $212.90  
  Purchase #4 $123.49   11.359%   $137.5172   $137.52   $137.50   $137.50  
  Purchase #5 $109.94   13.823%   $125.137   $125.14   $125.15   $125.10  
  Purchase #6 $65.91   6.446%   $70.1586   $70.16   $70.15   $70.20  
  Purchase #7 $226.56   5.803%   $239.7073   $239.71   $239.70   $239.70  
  7 purchase totals = $1,154.04       $1,254.2392   $1,254.25   $1,254.25   $1,254.20