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 $169.52   9.743%   $186.0363   $186.04   $186.05   $186.00  
  Purchase #2 $101.30   7.858%   $109.2602   $109.26   $109.25   $109.30  
  Purchase #3 $54.82   3.427%   $56.6987   $56.70   $56.70   $56.70  
  Purchase #4 $244.31   7.265%   $262.0591   $262.06   $262.05   $262.10  
  Purchase #5 $61.30   6.217%   $65.111   $65.11   $65.10   $65.10  
  Purchase #6 $161.56   6.761%   $172.4831   $172.48   $172.50   $172.50  
  Purchase #7 $136.44   5.653%   $144.153   $144.15   $144.15   $144.20  
  7 purchase totals = $929.25       $995.8014   $995.80   $995.80   $995.90