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 $203.77   11.551%   $227.3075   $227.31   $227.30   $227.30  
  Purchase #2 $119.96   3.594%   $124.2714   $124.27   $124.25   $124.30  
  Purchase #3 $19.71   5.234%   $20.7416   $20.74   $20.75   $20.70  
  Purchase #4 $77.41   6.650%   $82.5578   $82.56   $82.55   $82.60  
  Purchase #5 $45.76   4.750%   $47.9336   $47.93   $47.95   $47.90  
  Purchase #6 $210.45   7.489%   $226.2106   $226.21   $226.20   $226.20  
  Purchase #7 $110.25   12.469%   $123.9971   $124.00   $124.00   $124.00  
  7 purchase totals = $787.31       $853.0196   $853.02   $853.00   $853.00