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 $25.75   13.471%   $29.2188   $29.22   $29.20   $29.20  
  Purchase #2 $133.47   8.223%   $144.4452   $144.45   $144.45   $144.40  
  Purchase #3 $45.97   11.221%   $51.1283   $51.13   $51.15   $51.10  
  Purchase #4 $55.52   11.624%   $61.9736   $61.97   $61.95   $62.00  
  Purchase #5 $37.77   9.143%   $41.2233   $41.22   $41.20   $41.20  
  Purchase #6 $65.39   6.837%   $69.8607   $69.86   $69.85   $69.90  
  Purchase #7 $56.57   8.869%   $61.5872   $61.59   $61.60   $61.60  
  7 purchase totals = $420.44       $459.4371   $459.44   $459.40   $459.40