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 $48.52   7.303%   $52.0634   $52.06   $52.05   $52.10  
  Purchase #2 $147.35   5.785%   $155.8742   $155.87   $155.85   $155.90  
  Purchase #3 $248.36   12.242%   $278.7642   $278.76   $278.75   $278.80  
  Purchase #4 $156.71   6.723%   $167.2456   $167.25   $167.25   $167.20  
  Purchase #5 $58.58   12.477%   $65.889   $65.89   $65.90   $65.90  
  Purchase #6 $145.78   12.120%   $163.4485   $163.45   $163.45   $163.40  
  Purchase #7 $110.47   11.652%   $123.342   $123.34   $123.35   $123.30  
  7 purchase totals = $915.77       $1,006.6269   $1,006.62   $1,006.60   $1,006.60