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 $153.59   13.263%   $173.9606   $173.96   $173.95   $174.00  
  Purchase #2 $139.80   8.423%   $151.5754   $151.58   $151.60   $151.60  
  Purchase #3 $103.92   13.867%   $118.3306   $118.33   $118.35   $118.30  
  Purchase #4 $174.41   11.573%   $194.5945   $194.59   $194.60   $194.60  
  Purchase #5 $167.45   10.819%   $185.5664   $185.57   $185.55   $185.60  
  Purchase #6 $68.86   7.627%   $74.112   $74.11   $74.10   $74.10  
  Purchase #7 $248.52   12.500%   $279.585   $279.59   $279.60   $279.60  
  7 purchase totals = $1,056.55       $1,177.7245   $1,177.73   $1,177.75   $1,177.80