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 $58.57   4.124%   $60.9854   $60.99   $61.00   $61.00  
  Purchase #2 $179.90   13.266%   $203.7655   $203.77   $203.75   $203.80  
  Purchase #3 $180.58   11.771%   $201.8361   $201.84   $201.85   $201.80  
  Purchase #4 $48.26   7.612%   $51.9336   $51.93   $51.95   $51.90  
  Purchase #5 $102.86   13.553%   $116.8006   $116.80   $116.80   $116.80  
  Purchase #6 $235.95   5.821%   $249.6846   $249.68   $249.70   $249.70  
  Purchase #7 $229.94   4.631%   $240.5885   $240.59   $240.60   $240.60  
  7 purchase totals = $1,036.06       $1,125.5943   $1,125.60   $1,125.65   $1,125.60