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 $84.45   10.757%   $93.5343   $93.53   $93.55   $93.50  
  Purchase #2 $235.88   3.375%   $243.841   $243.84   $243.85   $243.80  
  Purchase #3 $127.48   4.229%   $132.8711   $132.87   $132.85   $132.90  
  Purchase #4 $147.59   5.532%   $155.7547   $155.75   $155.75   $155.80  
  Purchase #5 $222.60   8.432%   $241.3696   $241.37   $241.35   $241.40  
  Purchase #6 $229.33   11.486%   $255.6708   $255.67   $255.65   $255.70  
  Purchase #7 $33.96   13.743%   $38.6271   $38.63   $38.65   $38.60  
  7 purchase totals = $1,081.29       $1,161.6686   $1,161.66   $1,161.65   $1,161.70