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 $241.80   8.682%   $262.7931   $262.79   $262.80   $262.80  
  Purchase #2 $23.93   11.436%   $26.6666   $26.67   $26.65   $26.70  
  Purchase #3 $138.88   9.594%   $152.2041   $152.20   $152.20   $152.20  
  Purchase #4 $92.80   3.127%   $95.7019   $95.70   $95.70   $95.70  
  Purchase #5 $190.85   11.852%   $213.4695   $213.47   $213.45   $213.50  
  Purchase #6 $94.47   8.518%   $102.517   $102.52   $102.50   $102.50  
  Purchase #7 $40.29   13.689%   $45.8053   $45.81   $45.80   $45.80  
  7 purchase totals = $823.02       $899.1575   $899.16   $899.10   $899.20