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 $218.99   7.339%   $235.0617   $235.06   $235.05   $235.10  
  Purchase #2 $190.75   7.610%   $205.2661   $205.27   $205.25   $205.30  
  Purchase #3 $84.86   9.595%   $93.0023   $93.00   $93.00   $93.00  
  Purchase #4 $227.96   8.471%   $247.2705   $247.27   $247.25   $247.30  
  Purchase #5 $14.82   11.453%   $16.5173   $16.52   $16.50   $16.50  
  Purchase #6 $7.70   4.522%   $8.0482   $8.05   $8.05   $8.00  
  Purchase #7 $200.84   12.414%   $225.7723   $225.77   $225.75   $225.80  
  7 purchase totals = $945.92       $1,030.9384   $1,030.94   $1,030.85   $1,031.00