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 $228.44   8.780%   $248.497   $248.50   $248.50   $248.50  
  Purchase #2 $219.36   12.439%   $246.6462   $246.65   $246.65   $246.60  
  Purchase #3 $179.79   13.203%   $203.5277   $203.53   $203.55   $203.50  
  Purchase #4 $232.54   13.297%   $263.4608   $263.46   $263.45   $263.50  
  Purchase #5 $21.35   8.754%   $23.219   $23.22   $23.20   $23.20  
  Purchase #6 $117.32   8.697%   $127.5233   $127.52   $127.50   $127.50  
  Purchase #7 $145.53   6.713%   $155.2994   $155.30   $155.30   $155.30  
  7 purchase totals = $1,144.33       $1,268.1734   $1,268.18   $1,268.15   $1,268.10