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 $184.29   4.816%   $193.1654   $193.17   $193.15   $193.20  
  Purchase #2 $28.98   3.231%   $29.9163   $29.92   $29.90   $29.90  
  Purchase #3 $192.25   3.446%   $198.8749   $198.87   $198.85   $198.90  
  Purchase #4 $29.60   13.237%   $33.5182   $33.52   $33.50   $33.50  
  Purchase #5 $226.45   3.723%   $234.8807   $234.88   $234.90   $234.90  
  Purchase #6 $214.52   13.504%   $243.4888   $243.49   $243.50   $243.50  
  Purchase #7 $89.53   3.823%   $92.9527   $92.95   $92.95   $93.00  
  7 purchase totals = $965.62       $1,026.7970   $1,026.80   $1,026.75   $1,026.90