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 $53.51   10.776%   $59.2762   $59.28   $59.30   $59.30  
  Purchase #2 $232.58   13.486%   $263.9457   $263.95   $263.95   $263.90  
  Purchase #3 $214.31   8.537%   $232.6056   $232.61   $232.60   $232.60  
  Purchase #4 $40.52   5.324%   $42.6773   $42.68   $42.70   $42.70  
  Purchase #5 $121.57   4.658%   $127.2327   $127.23   $127.25   $127.20  
  Purchase #6 $222.94   3.446%   $230.6225   $230.62   $230.60   $230.60  
  Purchase #7 $110.90   13.608%   $125.9913   $125.99   $126.00   $126.00  
  7 purchase totals = $996.33       $1,082.3513   $1,082.36   $1,082.40   $1,082.30