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 $232.74   11.828%   $260.2685   $260.27   $260.25   $260.30  
  Purchase #2 $230.34   9.343%   $251.8607   $251.86   $251.85   $251.90  
  Purchase #3 $129.80   10.614%   $143.577   $143.58   $143.60   $143.60  
  Purchase #4 $64.48   9.770%   $70.7797   $70.78   $70.80   $70.80  
  Purchase #5 $104.39   9.190%   $113.9834   $113.98   $114.00   $114.00  
  Purchase #6 $80.51   7.357%   $86.4331   $86.43   $86.45   $86.40  
  Purchase #7 $147.61   5.220%   $155.3152   $155.32   $155.30   $155.30  
  7 purchase totals = $989.87       $1,082.2176   $1,082.22   $1,082.25   $1,082.30