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 $54.79   9.148%   $59.8022   $59.80   $59.80   $59.80  
  Purchase #2 $239.90   3.471%   $248.2269   $248.23   $248.25   $248.20  
  Purchase #3 $167.77   7.372%   $180.138   $180.14   $180.15   $180.10  
  Purchase #4 $54.28   10.773%   $60.1276   $60.13   $60.15   $60.10  
  Purchase #5 $11.86   10.565%   $13.113   $13.11   $13.10   $13.10  
  Purchase #6 $60.28   6.166%   $63.9969   $64.00   $64.00   $64.00  
  Purchase #7 $219.57   13.150%   $248.4435   $248.44   $248.45   $248.40  
  7 purchase totals = $808.45       $873.8481   $873.85   $873.90   $873.70