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 $209.40   12.213%   $234.974   $234.97   $234.95   $235.00  
  Purchase #2 $213.52   13.197%   $241.6982   $241.70   $241.70   $241.70  
  Purchase #3 $47.52   11.169%   $52.8275   $52.83   $52.85   $52.80  
  Purchase #4 $231.36   5.108%   $243.1779   $243.18   $243.20   $243.20  
  Purchase #5 $154.71   5.610%   $163.3892   $163.39   $163.40   $163.40  
  Purchase #6 $150.70   11.225%   $167.6161   $167.62   $167.60   $167.60  
  Purchase #7 $216.76   6.342%   $230.5069   $230.51   $230.50   $230.50  
  7 purchase totals = $1,223.97       $1,334.1898   $1,334.20   $1,334.20   $1,334.20