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 $87.95   12.462%   $98.9103   $98.91   $98.90   $98.90  
  Purchase #2 $161.31   5.351%   $169.9417   $169.94   $169.95   $169.90  
  Purchase #3 $50.91   11.805%   $56.9199   $56.92   $56.90   $56.90  
  Purchase #4 $160.73   13.229%   $181.993   $181.99   $182.00   $182.00  
  Purchase #5 $172.47   7.459%   $185.3345   $185.33   $185.35   $185.30  
  Purchase #6 $222.52   8.498%   $241.4297   $241.43   $241.45   $241.40  
  Purchase #7 $97.33   10.305%   $107.3599   $107.36   $107.35   $107.40  
  7 purchase totals = $953.22       $1,041.8890   $1,041.88   $1,041.90   $1,041.80