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 $245.82   7.856%   $265.1316   $265.13   $265.15   $265.10  
  Purchase #2 $169.81   13.643%   $192.9772   $192.98   $193.00   $193.00  
  Purchase #3 $229.34   12.788%   $258.668   $258.67   $258.65   $258.70  
  Purchase #4 $11.62   6.619%   $12.3891   $12.39   $12.40   $12.40  
  Purchase #5 $225.77   12.316%   $253.5758   $253.58   $253.60   $253.60  
  Purchase #6 $137.29   6.222%   $145.8322   $145.83   $145.85   $145.80  
  Purchase #7 $228.43   3.297%   $235.9613   $235.96   $235.95   $236.00  
  7 purchase totals = $1,248.08       $1,364.5352   $1,364.54   $1,364.60   $1,364.60