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 $117.66   7.621%   $126.6269   $126.63   $126.65   $126.60  
  Purchase #2 $195.76   4.335%   $204.2462   $204.25   $204.25   $204.20  
  Purchase #3 $173.31   6.327%   $184.2753   $184.28   $184.30   $184.30  
  Purchase #4 $46.53   6.240%   $49.4335   $49.43   $49.45   $49.40  
  Purchase #5 $133.77   10.308%   $147.559   $147.56   $147.55   $147.60  
  Purchase #6 $88.60   3.643%   $91.8277   $91.83   $91.85   $91.80  
  Purchase #7 $202.77   8.490%   $219.9852   $219.99   $220.00   $220.00  
  7 purchase totals = $958.40       $1,023.9538   $1,023.97   $1,024.05   $1,023.90