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 $173.43   11.834%   $193.9537   $193.95   $193.95   $194.00  
  Purchase #2 $113.27   6.326%   $120.4355   $120.44   $120.45   $120.40  
  Purchase #3 $202.26   4.626%   $211.6165   $211.62   $211.60   $211.60  
  Purchase #4 $132.68   11.377%   $147.775   $147.78   $147.80   $147.80  
  Purchase #5 $116.26   12.616%   $130.9274   $130.93   $130.95   $130.90  
  Purchase #6 $218.59   6.277%   $232.3109   $232.31   $232.30   $232.30  
  Purchase #7 $58.98   6.403%   $62.7565   $62.76   $62.75   $62.80  
  7 purchase totals = $1,015.47       $1,099.7755   $1,099.79   $1,099.80   $1,099.80