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 $169.76   13.174%   $192.1242   $192.12   $192.10   $192.10  
  Purchase #2 $246.39   6.731%   $262.9745   $262.97   $262.95   $263.00  
  Purchase #3 $204.54   10.346%   $225.7017   $225.70   $225.70   $225.70  
  Purchase #4 $147.39   8.163%   $159.4214   $159.42   $159.40   $159.40  
  Purchase #5 $50.99   4.369%   $53.2178   $53.22   $53.20   $53.20  
  Purchase #6 $176.29   7.612%   $189.7092   $189.71   $189.70   $189.70  
  Purchase #7 $153.38   13.178%   $173.5924   $173.59   $173.60   $173.60  
  7 purchase totals = $1,148.74       $1,256.7412   $1,256.73   $1,256.65   $1,256.70