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 $54.32   4.127%   $56.5618   $56.56   $56.55   $56.60  
  Purchase #2 $228.83   7.216%   $245.3424   $245.34   $245.35   $245.30  
  Purchase #3 $130.34   7.459%   $140.0621   $140.06   $140.05   $140.10  
  Purchase #4 $85.65   10.421%   $94.5756   $94.58   $94.60   $94.60  
  Purchase #5 $95.60   6.616%   $101.9249   $101.92   $101.90   $101.90  
  Purchase #6 $171.52   8.657%   $186.3685   $186.37   $186.35   $186.40  
  Purchase #7 $47.72   4.250%   $49.7481   $49.75   $49.75   $49.70  
  7 purchase totals = $813.98       $874.5834   $874.58   $874.55   $874.60