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 $183.97   4.676%   $192.5724   $192.57   $192.55   $192.60  
  Purchase #2 $25.65   4.108%   $26.7037   $26.70   $26.70   $26.70  
  Purchase #3 $150.74   10.403%   $166.4215   $166.42   $166.40   $166.40  
  Purchase #4 $234.90   10.492%   $259.5457   $259.55   $259.55   $259.50  
  Purchase #5 $24.54   5.747%   $25.9503   $25.95   $25.95   $26.00  
  Purchase #6 $223.52   5.727%   $236.321   $236.32   $236.30   $236.30  
  Purchase #7 $238.52   8.514%   $258.8276   $258.83   $258.85   $258.80  
  7 purchase totals = $1,081.84       $1,166.3422   $1,166.34   $1,166.30   $1,166.30