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 $66.69   6.793%   $71.2203   $71.22   $71.20   $71.20  
  Purchase #2 $153.60   10.488%   $169.7096   $169.71   $169.70   $169.70  
  Purchase #3 $49.83   12.563%   $56.0901   $56.09   $56.10   $56.10  
  Purchase #4 $219.56   10.720%   $243.0968   $243.10   $243.10   $243.10  
  Purchase #5 $229.37   8.461%   $248.777   $248.78   $248.80   $248.80  
  Purchase #6 $103.97   5.585%   $109.7767   $109.78   $109.80   $109.80  
  Purchase #7 $47.52   9.444%   $52.0078   $52.01   $52.00   $52.00  
  7 purchase totals = $870.54       $950.6783   $950.69   $950.70   $950.70