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 $61.58   12.683%   $69.3902   $69.39   $69.40   $69.40  
  Purchase #2 $241.66   10.647%   $267.3895   $267.39   $267.40   $267.40  
  Purchase #3 $193.89   8.231%   $209.8491   $209.85   $209.85   $209.80  
  Purchase #4 $226.71   7.333%   $243.3346   $243.33   $243.35   $243.30  
  Purchase #5 $53.98   4.436%   $56.3746   $56.37   $56.35   $56.40  
  Purchase #6 $77.32   9.421%   $84.6043   $84.60   $84.60   $84.60  
  Purchase #7 $211.55   5.416%   $223.0075   $223.01   $223.00   $223.00  
  7 purchase totals = $1,066.69       $1,153.9498   $1,153.94   $1,153.95   $1,153.90