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 $179.77   7.653%   $193.5278   $193.53   $193.55   $193.50  
  Purchase #2 $53.74   9.751%   $58.9802   $58.98   $59.00   $59.00  
  Purchase #3 $157.95   6.244%   $167.8124   $167.81   $167.80   $167.80  
  Purchase #4 $156.41   6.871%   $167.1569   $167.16   $167.15   $167.20  
  Purchase #5 $84.93   13.422%   $96.3293   $96.33   $96.35   $96.30  
  Purchase #6 $5.76   5.206%   $6.0599   $6.06   $6.05   $6.10  
  Purchase #7 $138.91   3.304%   $143.4996   $143.50   $143.50   $143.50  
  7 purchase totals = $777.47       $833.3661   $833.37   $833.40   $833.40