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 $143.52   6.470%   $152.8057   $152.81   $152.80   $152.80  
  Purchase #2 $163.55   9.604%   $179.2573   $179.26   $179.25   $179.30  
  Purchase #3 $243.97   10.214%   $268.8891   $268.89   $268.90   $268.90  
  Purchase #4 $191.41   5.161%   $201.2887   $201.29   $201.30   $201.30  
  Purchase #5 $95.89   13.351%   $108.6923   $108.69   $108.70   $108.70  
  Purchase #6 $8.26   8.227%   $8.9396   $8.94   $8.95   $8.90  
  Purchase #7 $83.40   13.503%   $94.6615   $94.66   $94.65   $94.70  
  7 purchase totals = $930.00       $1,014.5342   $1,014.54   $1,014.55   $1,014.60