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 $76.49   10.504%   $84.5245   $84.52   $84.50   $84.50  
  Purchase #2 $18.60   10.627%   $20.5766   $20.58   $20.60   $20.60  
  Purchase #3 $67.45   10.809%   $74.7407   $74.74   $74.75   $74.70  
  Purchase #4 $83.86   9.342%   $91.6942   $91.69   $91.70   $91.70  
  Purchase #5 $155.74   8.237%   $168.5683   $168.57   $168.55   $168.60  
  Purchase #6 $5.54   8.204%   $5.9945   $5.99   $6.00   $6.00  
  Purchase #7 $17.74   11.803%   $19.8339   $19.83   $19.85   $19.80  
  7 purchase totals = $425.42       $465.9327   $465.92   $465.95   $465.90