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 $66.52   4.206%   $69.3178   $69.32   $69.30   $69.30  
  Purchase #2 $141.47   7.341%   $151.8553   $151.86   $151.85   $151.90  
  Purchase #3 $169.44   7.871%   $182.7766   $182.78   $182.80   $182.80  
  Purchase #4 $182.89   6.563%   $194.8931   $194.89   $194.90   $194.90  
  Purchase #5 $99.48   3.174%   $102.6375   $102.64   $102.65   $102.60  
  Purchase #6 $198.27   3.393%   $204.9973   $205.00   $205.00   $205.00  
  Purchase #7 $182.34   5.749%   $192.8227   $192.82   $192.80   $192.80  
  7 purchase totals = $1,040.41       $1,099.3003   $1,099.31   $1,099.30   $1,099.30