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 $63.89   8.424%   $69.2721   $69.27   $69.25   $69.30  
  Purchase #2 $113.52   12.546%   $127.7622   $127.76   $127.75   $127.80  
  Purchase #3 $195.51   5.263%   $205.7997   $205.80   $205.80   $205.80  
  Purchase #4 $212.35   8.214%   $229.7924   $229.79   $229.80   $229.80  
  Purchase #5 $15.42   8.395%   $16.7145   $16.71   $16.70   $16.70  
  Purchase #6 $75.55   7.127%   $80.9344   $80.93   $80.95   $80.90  
  Purchase #7 $205.52   12.488%   $231.1853   $231.19   $231.20   $231.20  
  7 purchase totals = $881.76       $961.4606   $961.45   $961.45   $961.50