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 $22.48   12.255%   $25.2349   $25.23   $25.25   $25.20  
  Purchase #2 $231.52   8.718%   $251.7039   $251.70   $251.70   $251.70  
  Purchase #3 $224.31   9.607%   $245.8595   $245.86   $245.85   $245.90  
  Purchase #4 $65.27   6.349%   $69.414   $69.41   $69.40   $69.40  
  Purchase #5 $148.82   3.531%   $154.0748   $154.07   $154.05   $154.10  
  Purchase #6 $48.58   12.461%   $54.6336   $54.63   $54.65   $54.60  
  Purchase #7 $134.28   8.262%   $145.3742   $145.37   $145.35   $145.40  
  7 purchase totals = $875.26       $946.2949   $946.27   $946.25   $946.30