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 $189.64   6.433%   $201.8395   $201.84   $201.85   $201.80  
  Purchase #2 $60.89   10.162%   $67.0776   $67.08   $67.10   $67.10  
  Purchase #3 $173.68   7.646%   $186.9596   $186.96   $186.95   $187.00  
  Purchase #4 $59.69   6.542%   $63.5949   $63.59   $63.60   $63.60  
  Purchase #5 $97.49   3.645%   $101.0435   $101.04   $101.05   $101.00  
  Purchase #6 $12.72   5.354%   $13.401   $13.40   $13.40   $13.40  
  Purchase #7 $240.49   12.417%   $270.3516   $270.35   $270.35   $270.40  
  7 purchase totals = $834.60       $904.2677   $904.26   $904.30   $904.30