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 $90.64   13.286%   $102.6824   $102.68   $102.70   $102.70  
  Purchase #2 $203.87   5.188%   $214.4468   $214.45   $214.45   $214.40  
  Purchase #3 $59.99   11.180%   $66.6969   $66.70   $66.70   $66.70  
  Purchase #4 $123.31   9.642%   $135.1996   $135.20   $135.20   $135.20  
  Purchase #5 $144.57   6.746%   $154.3227   $154.32   $154.30   $154.30  
  Purchase #6 $217.85   9.191%   $237.8726   $237.87   $237.85   $237.90  
  Purchase #7 $134.88   13.207%   $152.6936   $152.69   $152.70   $152.70  
  7 purchase totals = $975.11       $1,063.9146   $1,063.91   $1,063.90   $1,063.90