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 $219.79   12.709%   $247.7231   $247.72   $247.70   $247.70  
  Purchase #2 $41.63   4.861%   $43.6536   $43.65   $43.65   $43.70  
  Purchase #3 $122.29   13.107%   $138.3186   $138.32   $138.30   $138.30  
  Purchase #4 $59.76   6.253%   $63.4968   $63.50   $63.50   $63.50  
  Purchase #5 $144.40   5.169%   $151.864   $151.86   $151.85   $151.90  
  Purchase #6 $187.54   3.623%   $194.3346   $194.33   $194.35   $194.30  
  Purchase #7 $33.80   3.702%   $35.0513   $35.05   $35.05   $35.10  
  7 purchase totals = $809.21       $874.4420   $874.43   $874.40   $874.50