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 $213.53   3.115%   $220.1815   $220.18   $220.20   $220.20  
  Purchase #2 $170.42   3.543%   $176.458   $176.46   $176.45   $176.50  
  Purchase #3 $61.72   11.301%   $68.695   $68.70   $68.70   $68.70  
  Purchase #4 $36.42   13.416%   $41.3061   $41.31   $41.30   $41.30  
  Purchase #5 $79.69   9.544%   $87.2956   $87.30   $87.30   $87.30  
  Purchase #6 $226.91   10.566%   $250.8853   $250.89   $250.90   $250.90  
  Purchase #7 $160.72   5.729%   $169.9276   $169.93   $169.95   $169.90  
  7 purchase totals = $949.41       $1,014.7491   $1,014.77   $1,014.80   $1,014.80