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 $134.81   12.556%   $151.7367   $151.74   $151.75   $151.70  
  Purchase #2 $88.45   8.710%   $96.154   $96.15   $96.15   $96.20  
  Purchase #3 $233.84   10.128%   $257.5233   $257.52   $257.50   $257.50  
  Purchase #4 $117.96   12.427%   $132.6189   $132.62   $132.60   $132.60  
  Purchase #5 $81.68   3.189%   $84.2848   $84.28   $84.30   $84.30  
  Purchase #6 $246.45   3.190%   $254.3118   $254.31   $254.30   $254.30  
  Purchase #7 $73.90   5.405%   $77.8943   $77.89   $77.90   $77.90  
  7 purchase totals = $977.09       $1,054.5238   $1,054.51   $1,054.50   $1,054.50