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 $61.56   7.710%   $66.3063   $66.31   $66.30   $66.30  
  Purchase #2 $216.90   8.553%   $235.4515   $235.45   $235.45   $235.50  
  Purchase #3 $223.71   10.615%   $247.4568   $247.46   $247.45   $247.50  
  Purchase #4 $228.75   9.731%   $251.0097   $251.01   $251.00   $251.00  
  Purchase #5 $188.89   7.133%   $202.3635   $202.36   $202.35   $202.40  
  Purchase #6 $10.58   9.777%   $11.6144   $11.61   $11.60   $11.60  
  Purchase #7 $219.83   6.648%   $234.4443   $234.44   $234.45   $234.40  
  7 purchase totals = $1,150.22       $1,248.6465   $1,248.64   $1,248.60   $1,248.70