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 $201.71   11.783%   $225.4775   $225.48   $225.50   $225.50  
  Purchase #2 $247.40   9.687%   $271.3656   $271.37   $271.35   $271.40  
  Purchase #3 $181.25   12.286%   $203.5184   $203.52   $203.50   $203.50  
  Purchase #4 $190.51   4.210%   $198.5305   $198.53   $198.55   $198.50  
  Purchase #5 $54.98   10.320%   $60.6539   $60.65   $60.65   $60.70  
  Purchase #6 $232.85   10.721%   $257.8138   $257.81   $257.80   $257.80  
  Purchase #7 $53.28   11.783%   $59.558   $59.56   $59.55   $59.60  
  7 purchase totals = $1,161.98       $1,276.9177   $1,276.92   $1,276.90   $1,277.00