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 $54.30   13.765%   $61.7744   $61.77   $61.75   $61.80  
  Purchase #2 $204.96   8.489%   $222.3591   $222.36   $222.35   $222.40  
  Purchase #3 $138.71   7.575%   $149.2173   $149.22   $149.20   $149.20  
  Purchase #4 $235.90   10.684%   $261.1036   $261.10   $261.10   $261.10  
  Purchase #5 $108.39   4.280%   $113.0291   $113.03   $113.05   $113.00  
  Purchase #6 $249.69   8.391%   $270.6415   $270.64   $270.65   $270.60  
  Purchase #7 $145.72   10.549%   $161.092   $161.09   $161.10   $161.10  
  7 purchase totals = $1,137.67       $1,239.2170   $1,239.21   $1,239.20   $1,239.20