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 $45.81   13.407%   $51.9517   $51.95   $51.95   $52.00  
  Purchase #2 $168.58   8.572%   $183.0307   $183.03   $183.05   $183.00  
  Purchase #3 $48.55   11.856%   $54.3061   $54.31   $54.30   $54.30  
  Purchase #4 $117.64   7.155%   $126.0571   $126.06   $126.05   $126.10  
  Purchase #5 $103.85   6.475%   $110.5743   $110.57   $110.55   $110.60  
  Purchase #6 $169.84   10.323%   $187.3726   $187.37   $187.35   $187.40  
  Purchase #7 $73.99   8.525%   $80.2976   $80.30   $80.30   $80.30  
  7 purchase totals = $728.26       $793.5901   $793.59   $793.55   $793.70