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 $87.33   13.360%   $98.9973   $99.00   $99.00   $99.00  
  Purchase #2 $185.28   11.186%   $206.0054   $206.01   $206.00   $206.00  
  Purchase #3 $61.90   4.841%   $64.8966   $64.90   $64.90   $64.90  
  Purchase #4 $246.26   9.568%   $269.8222   $269.82   $269.80   $269.80  
  Purchase #5 $215.62   12.687%   $242.9757   $242.98   $243.00   $243.00  
  Purchase #6 $159.70   12.701%   $179.9835   $179.98   $180.00   $180.00  
  Purchase #7 $48.65   4.349%   $50.7658   $50.77   $50.75   $50.80  
  7 purchase totals = $1,004.74       $1,113.4465   $1,113.46   $1,113.45   $1,113.50