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 $61.92   13.173%   $70.0767   $70.08   $70.10   $70.10  
  Purchase #2 $141.29   13.474%   $160.3274   $160.33   $160.35   $160.30  
  Purchase #3 $229.99   9.693%   $252.2829   $252.28   $252.30   $252.30  
  Purchase #4 $60.39   8.465%   $65.502   $65.50   $65.50   $65.50  
  Purchase #5 $203.39   5.865%   $215.3188   $215.32   $215.30   $215.30  
  Purchase #6 $185.90   9.317%   $203.2203   $203.22   $203.20   $203.20  
  Purchase #7 $100.99   7.352%   $108.4148   $108.41   $108.40   $108.40  
  7 purchase totals = $983.87       $1,075.1429   $1,075.14   $1,075.15   $1,075.10