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 $244.34   6.677%   $260.6546   $260.65   $260.65   $260.70  
  Purchase #2 $182.40   5.234%   $191.9468   $191.95   $191.95   $191.90  
  Purchase #3 $151.81   12.692%   $171.0777   $171.08   $171.10   $171.10  
  Purchase #4 $57.89   9.788%   $63.5563   $63.56   $63.55   $63.60  
  Purchase #5 $209.80   6.706%   $223.8692   $223.87   $223.85   $223.90  
  Purchase #6 $80.35   8.651%   $87.3011   $87.30   $87.30   $87.30  
  Purchase #7 $192.92   5.862%   $204.229   $204.23   $204.25   $204.20  
  7 purchase totals = $1,119.51       $1,202.6347   $1,202.64   $1,202.65   $1,202.70