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 $44.92   12.702%   $50.6257   $50.63   $50.65   $50.60  
  Purchase #2 $174.72   6.807%   $186.6132   $186.61   $186.60   $186.60  
  Purchase #3 $48.72   7.819%   $52.5294   $52.53   $52.55   $52.50  
  Purchase #4 $196.52   6.838%   $209.958   $209.96   $209.95   $210.00  
  Purchase #5 $156.79   10.488%   $173.2341   $173.23   $173.25   $173.20  
  Purchase #6 $182.51   12.819%   $205.906   $205.91   $205.90   $205.90  
  Purchase #7 $169.26   6.128%   $179.6323   $179.63   $179.65   $179.60  
  7 purchase totals = $973.44       $1,058.4987   $1,058.50   $1,058.55   $1,058.40