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 $214.80   9.486%   $235.1759   $235.18   $235.20   $235.20  
  Purchase #2 $5.37   11.492%   $5.9871   $5.99   $6.00   $6.00  
  Purchase #3 $181.52   13.173%   $205.4316   $205.43   $205.45   $205.40  
  Purchase #4 $223.88   4.845%   $234.727   $234.73   $234.75   $234.70  
  Purchase #5 $52.32   9.610%   $57.348   $57.35   $57.35   $57.30  
  Purchase #6 $244.32   10.253%   $269.3701   $269.37   $269.35   $269.40  
  Purchase #7 $198.97   13.193%   $225.2201   $225.22   $225.20   $225.20  
  7 purchase totals = $1,121.18       $1,233.2598   $1,233.27   $1,233.30   $1,233.20