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 $241.54   7.508%   $259.6748   $259.67   $259.65   $259.70  
  Purchase #2 $114.48   6.158%   $121.5297   $121.53   $121.55   $121.50  
  Purchase #3 $120.52   5.205%   $126.7931   $126.79   $126.80   $126.80  
  Purchase #4 $102.62   3.623%   $106.3379   $106.34   $106.35   $106.30  
  Purchase #5 $48.71   8.850%   $53.0208   $53.02   $53.00   $53.00  
  Purchase #6 $44.96   11.763%   $50.2486   $50.25   $50.25   $50.20  
  Purchase #7 $93.81   5.331%   $98.811   $98.81   $98.80   $98.80  
  7 purchase totals = $766.64       $816.4159   $816.41   $816.40   $816.30