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 $51.76   9.294%   $56.5706   $56.57   $56.55   $56.60  
  Purchase #2 $166.53   4.437%   $173.9189   $173.92   $173.90   $173.90  
  Purchase #3 $227.79   3.873%   $236.6123   $236.61   $236.60   $236.60  
  Purchase #4 $166.98   3.262%   $172.4269   $172.43   $172.45   $172.40  
  Purchase #5 $151.28   8.159%   $163.6229   $163.62   $163.60   $163.60  
  Purchase #6 $135.40   11.310%   $150.7137   $150.71   $150.70   $150.70  
  Purchase #7 $216.56   4.842%   $227.0458   $227.05   $227.05   $227.00  
  7 purchase totals = $1,116.30       $1,180.9111   $1,180.91   $1,180.85   $1,180.80