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 $59.41   7.471%   $63.8485   $63.85   $63.85   $63.80  
  Purchase #2 $220.45   10.643%   $243.9125   $243.91   $243.90   $243.90  
  Purchase #3 $250.84   8.368%   $271.8303   $271.83   $271.85   $271.80  
  Purchase #4 $144.89   5.599%   $153.0024   $153.00   $153.00   $153.00  
  Purchase #5 $226.99   6.544%   $241.8442   $241.84   $241.85   $241.80  
  Purchase #6 $120.46   9.491%   $131.8929   $131.89   $131.90   $131.90  
  Purchase #7 $192.52   10.313%   $212.3746   $212.37   $212.35   $212.40  
  7 purchase totals = $1,215.56       $1,318.7054   $1,318.69   $1,318.70   $1,318.60