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 $173.66   11.220%   $193.1447   $193.14   $193.15   $193.10  
  Purchase #2 $241.79   4.342%   $252.2885   $252.29   $252.30   $252.30  
  Purchase #3 $95.74   10.230%   $105.5342   $105.53   $105.55   $105.50  
  Purchase #4 $43.28   5.716%   $45.7539   $45.75   $45.75   $45.80  
  Purchase #5 $74.72   10.798%   $82.7883   $82.79   $82.80   $82.80  
  Purchase #6 $210.30   12.783%   $237.1826   $237.18   $237.20   $237.20  
  Purchase #7 $120.68   9.263%   $131.8586   $131.86   $131.85   $131.90  
  7 purchase totals = $960.17       $1,048.5508   $1,048.54   $1,048.60   $1,048.60