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 $202.27   5.549%   $213.494   $213.49   $213.50   $213.50  
  Purchase #2 $31.98   10.638%   $35.382   $35.38   $35.40   $35.40  
  Purchase #3 $160.29   9.463%   $175.4582   $175.46   $175.45   $175.50  
  Purchase #4 $159.91   9.585%   $175.2374   $175.24   $175.25   $175.20  
  Purchase #5 $90.46   11.252%   $100.6386   $100.64   $100.65   $100.60  
  Purchase #6 $110.58   9.754%   $121.366   $121.37   $121.35   $121.40  
  Purchase #7 $210.32   6.326%   $223.6248   $223.62   $223.60   $223.60  
  7 purchase totals = $965.81       $1,045.2010   $1,045.20   $1,045.20   $1,045.20