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 $57.71   5.262%   $60.7467   $60.75   $60.75   $60.70  
  Purchase #2 $31.43   13.431%   $35.6514   $35.65   $35.65   $35.70  
  Purchase #3 $192.91   10.138%   $212.4672   $212.47   $212.45   $212.50  
  Purchase #4 $126.68   13.294%   $143.5208   $143.52   $143.50   $143.50  
  Purchase #5 $139.40   11.503%   $155.4352   $155.44   $155.45   $155.40  
  Purchase #6 $187.81   12.236%   $210.7904   $210.79   $210.80   $210.80  
  Purchase #7 $5.62   9.235%   $6.139   $6.14   $6.15   $6.10  
  7 purchase totals = $741.56       $824.7507   $824.76   $824.75   $824.70