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 $249.27   7.436%   $267.8057   $267.81   $267.80   $267.80  
  Purchase #2 $68.33   9.515%   $74.8316   $74.83   $74.85   $74.80  
  Purchase #3 $59.80   10.802%   $66.2596   $66.26   $66.25   $66.30  
  Purchase #4 $157.52   9.291%   $172.1552   $172.16   $172.15   $172.20  
  Purchase #5 $207.26   9.366%   $226.672   $226.67   $226.65   $226.70  
  Purchase #6 $184.29   9.787%   $202.3265   $202.33   $202.35   $202.30  
  Purchase #7 $62.49   8.140%   $67.5767   $67.58   $67.60   $67.60  
  7 purchase totals = $988.96       $1,077.6273   $1,077.64   $1,077.65   $1,077.70