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 $245.57   11.822%   $274.6013   $274.60   $274.60   $274.60  
  Purchase #2 $61.95   10.623%   $68.5309   $68.53   $68.55   $68.50  
  Purchase #3 $70.25   4.769%   $73.6002   $73.60   $73.60   $73.60  
  Purchase #4 $102.52   13.321%   $116.1767   $116.18   $116.20   $116.20  
  Purchase #5 $171.39   8.702%   $186.3044   $186.30   $186.30   $186.30  
  Purchase #6 $194.96   13.831%   $221.9249   $221.92   $221.90   $221.90  
  Purchase #7 $74.98   9.523%   $82.1203   $82.12   $82.10   $82.10  
  7 purchase totals = $921.62       $1,023.2587   $1,023.25   $1,023.25   $1,023.20