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 $205.60   9.543%   $225.2204   $225.22   $225.20   $225.20  
  Purchase #2 $80.36   10.157%   $88.5222   $88.52   $88.50   $88.50  
  Purchase #3 $215.81   4.549%   $225.6272   $225.63   $225.65   $225.60  
  Purchase #4 $88.85   8.701%   $96.5808   $96.58   $96.60   $96.60  
  Purchase #5 $8.55   8.317%   $9.2611   $9.26   $9.25   $9.30  
  Purchase #6 $201.49   5.356%   $212.2818   $212.28   $212.30   $212.30  
  Purchase #7 $140.47   8.368%   $152.2245   $152.22   $152.20   $152.20  
  7 purchase totals = $941.13       $1,009.7180   $1,009.71   $1,009.70   $1,009.70