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 $168.90   12.677%   $190.3115   $190.31   $190.30   $190.30  
  Purchase #2 $166.54   3.644%   $172.6087   $172.61   $172.60   $172.60  
  Purchase #3 $218.84   11.580%   $244.1817   $244.18   $244.20   $244.20  
  Purchase #4 $125.74   11.212%   $139.838   $139.84   $139.85   $139.80  
  Purchase #5 $128.54   5.426%   $135.5146   $135.51   $135.50   $135.50  
  Purchase #6 $143.32   5.690%   $151.4749   $151.47   $151.45   $151.50  
  Purchase #7 $169.77   6.587%   $180.9527   $180.95   $180.95   $181.00  
  7 purchase totals = $1,121.65       $1,214.8821   $1,214.87   $1,214.85   $1,214.90