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 $91.55   6.576%   $97.5703   $97.57   $97.55   $97.60  
  Purchase #2 $82.86   8.129%   $89.5957   $89.60   $89.60   $89.60  
  Purchase #3 $227.67   4.605%   $238.1542   $238.15   $238.15   $238.20  
  Purchase #4 $118.54   9.363%   $129.6389   $129.64   $129.65   $129.60  
  Purchase #5 $241.65   7.779%   $260.448   $260.45   $260.45   $260.40  
  Purchase #6 $60.28   11.103%   $66.9729   $66.97   $66.95   $67.00  
  Purchase #7 $214.40   5.615%   $226.4386   $226.44   $226.45   $226.40  
  7 purchase totals = $1,036.95       $1,108.8186   $1,108.82   $1,108.80   $1,108.80