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 $52.80   7.358%   $56.685   $56.69   $56.70   $56.70  
  Purchase #2 $81.47   8.698%   $88.5563   $88.56   $88.55   $88.60  
  Purchase #3 $146.52   12.779%   $165.2438   $165.24   $165.25   $165.20  
  Purchase #4 $212.57   8.162%   $229.92   $229.92   $229.90   $229.90  
  Purchase #5 $43.94   12.779%   $49.5551   $49.56   $49.55   $49.60  
  Purchase #6 $160.35   9.849%   $176.1429   $176.14   $176.15   $176.10  
  Purchase #7 $230.71   10.112%   $254.0394   $254.04   $254.05   $254.00  
  7 purchase totals = $928.36       $1,020.1425   $1,020.15   $1,020.15   $1,020.10