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 $223.25   5.341%   $235.1738   $235.17   $235.15   $235.20  
  Purchase #2 $166.67   7.352%   $178.9236   $178.92   $178.90   $178.90  
  Purchase #3 $187.49   9.150%   $204.6453   $204.65   $204.65   $204.60  
  Purchase #4 $17.51   11.612%   $19.5433   $19.54   $19.55   $19.50  
  Purchase #5 $64.28   6.189%   $68.2583   $68.26   $68.25   $68.30  
  Purchase #6 $182.60   3.654%   $189.2722   $189.27   $189.25   $189.30  
  Purchase #7 $120.34   3.772%   $124.8792   $124.88   $124.90   $124.90  
  7 purchase totals = $962.14       $1,020.6957   $1,020.69   $1,020.65   $1,020.70