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 $94.57   5.410%   $99.6862   $99.69   $99.70   $99.70  
  Purchase #2 $249.97   3.520%   $258.7689   $258.77   $258.75   $258.80  
  Purchase #3 $243.46   3.492%   $251.9616   $251.96   $251.95   $252.00  
  Purchase #4 $247.46   5.381%   $260.7758   $260.78   $260.80   $260.80  
  Purchase #5 $58.45   10.113%   $64.361   $64.36   $64.35   $64.40  
  Purchase #6 $176.95   8.724%   $192.3871   $192.39   $192.40   $192.40  
  Purchase #7 $212.40   7.679%   $228.7102   $228.71   $228.70   $228.70  
  7 purchase totals = $1,283.26       $1,356.6508   $1,356.66   $1,356.65   $1,356.80