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 $174.90   5.112%   $183.8409   $183.84   $183.85   $183.80  
  Purchase #2 $158.87   8.807%   $172.8617   $172.86   $172.85   $172.90  
  Purchase #3 $43.85   9.537%   $48.032   $48.03   $48.05   $48.00  
  Purchase #4 $190.66   10.776%   $211.2055   $211.21   $211.20   $211.20  
  Purchase #5 $95.43   13.348%   $108.168   $108.17   $108.15   $108.20  
  Purchase #6 $187.54   12.255%   $210.523   $210.52   $210.50   $210.50  
  Purchase #7 $60.82   10.223%   $67.0376   $67.04   $67.05   $67.00  
  7 purchase totals = $912.07       $1,001.6687   $1,001.67   $1,001.65   $1,001.60