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 $46.79   11.769%   $52.2967   $52.30   $52.30   $52.30  
  Purchase #2 $150.51   5.120%   $158.2161   $158.22   $158.20   $158.20  
  Purchase #3 $168.64   7.486%   $181.2644   $181.26   $181.25   $181.30  
  Purchase #4 $43.90   3.691%   $45.5203   $45.52   $45.50   $45.50  
  Purchase #5 $213.86   5.161%   $224.8973   $224.90   $224.90   $224.90  
  Purchase #6 $179.99   8.312%   $194.9508   $194.95   $194.95   $195.00  
  Purchase #7 $16.62   7.747%   $17.9076   $17.91   $17.90   $17.90  
  7 purchase totals = $820.31       $875.0532   $875.06   $875.00   $875.10