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 $204.59   10.315%   $225.6935   $225.69   $225.70   $225.70  
  Purchase #2 $190.35   12.546%   $214.2313   $214.23   $214.25   $214.20  
  Purchase #3 $192.55   9.561%   $210.9597   $210.96   $210.95   $211.00  
  Purchase #4 $84.66   7.121%   $90.6886   $90.69   $90.70   $90.70  
  Purchase #5 $26.55   8.668%   $28.8514   $28.85   $28.85   $28.90  
  Purchase #6 $153.59   7.201%   $164.65   $164.65   $164.65   $164.70  
  Purchase #7 $95.69   9.284%   $104.5739   $104.57   $104.55   $104.60  
  7 purchase totals = $947.98       $1,039.6484   $1,039.64   $1,039.65   $1,039.80