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 $149.78   9.112%   $163.428   $163.43   $163.45   $163.40  
  Purchase #2 $24.25   6.467%   $25.8182   $25.82   $25.80   $25.80  
  Purchase #3 $157.74   3.781%   $163.7041   $163.70   $163.70   $163.70  
  Purchase #4 $151.69   3.374%   $156.808   $156.81   $156.80   $156.80  
  Purchase #5 $200.84   12.567%   $226.0796   $226.08   $226.10   $226.10  
  Purchase #6 $127.30   3.381%   $131.604   $131.60   $131.60   $131.60  
  Purchase #7 $168.96   12.815%   $190.6122   $190.61   $190.60   $190.60  
  7 purchase totals = $980.56       $1,058.0541   $1,058.05   $1,058.05   $1,058.00