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 $244.33   8.122%   $264.1745   $264.17   $264.15   $264.20  
  Purchase #2 $194.52   6.835%   $207.8154   $207.82   $207.80   $207.80  
  Purchase #3 $97.45   12.571%   $109.7004   $109.70   $109.70   $109.70  
  Purchase #4 $182.44   12.166%   $204.6357   $204.64   $204.65   $204.60  
  Purchase #5 $155.88   5.593%   $164.5984   $164.60   $164.60   $164.60  
  Purchase #6 $164.51   6.217%   $174.7376   $174.74   $174.75   $174.70  
  Purchase #7 $120.34   3.782%   $124.8913   $124.89   $124.90   $124.90  
  7 purchase totals = $1,159.47       $1,250.5533   $1,250.56   $1,250.55   $1,250.50