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 $194.75   6.127%   $206.6823   $206.68   $206.70   $206.70  
  Purchase #2 $26.90   4.373%   $28.0763   $28.08   $28.10   $28.10  
  Purchase #3 $204.70   4.802%   $214.5297   $214.53   $214.55   $214.50  
  Purchase #4 $154.56   11.344%   $172.0933   $172.09   $172.10   $172.10  
  Purchase #5 $111.73   5.343%   $117.6997   $117.70   $117.70   $117.70  
  Purchase #6 $104.41   5.203%   $109.8425   $109.84   $109.85   $109.80  
  Purchase #7 $142.72   6.812%   $152.4421   $152.44   $152.45   $152.40  
  7 purchase totals = $939.77       $1,001.3659   $1,001.36   $1,001.45   $1,001.30