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 $36.76   13.402%   $41.6866   $41.69   $41.70   $41.70  
  Purchase #2 $167.89   5.415%   $176.9812   $176.98   $177.00   $177.00  
  Purchase #3 $130.33   5.625%   $137.6611   $137.66   $137.65   $137.70  
  Purchase #4 $179.26   12.419%   $201.5223   $201.52   $201.50   $201.50  
  Purchase #5 $213.64   10.350%   $235.7517   $235.75   $235.75   $235.80  
  Purchase #6 $97.85   5.264%   $103.0008   $103.00   $103.00   $103.00  
  Purchase #7 $209.80   4.455%   $219.1466   $219.15   $219.15   $219.10  
  7 purchase totals = $1,035.53       $1,115.7503   $1,115.75   $1,115.75   $1,115.80