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 $171.27   7.454%   $184.0365   $184.04   $184.05   $184.00  
  Purchase #2 $131.47   6.847%   $140.4718   $140.47   $140.45   $140.50  
  Purchase #3 $167.60   11.373%   $186.6611   $186.66   $186.65   $186.70  
  Purchase #4 $239.27   11.831%   $267.578   $267.58   $267.60   $267.60  
  Purchase #5 $132.47   13.718%   $150.6422   $150.64   $150.65   $150.60  
  Purchase #6 $22.31   13.573%   $25.3381   $25.34   $25.35   $25.30  
  Purchase #7 $153.40   3.239%   $158.3686   $158.37   $158.35   $158.40  
  7 purchase totals = $1,017.79       $1,113.0963   $1,113.10   $1,113.10   $1,113.10