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 $189.76   9.635%   $208.0434   $208.04   $208.05   $208.00  
  Purchase #2 $201.70   13.346%   $228.6189   $228.62   $228.60   $228.60  
  Purchase #3 $37.92   6.629%   $40.4337   $40.43   $40.45   $40.40  
  Purchase #4 $59.77   6.124%   $63.4303   $63.43   $63.45   $63.40  
  Purchase #5 $55.58   11.630%   $62.044   $62.04   $62.05   $62.00  
  Purchase #6 $247.30   4.564%   $258.5868   $258.59   $258.60   $258.60  
  Purchase #7 $170.32   6.830%   $181.9529   $181.95   $181.95   $182.00  
  7 purchase totals = $962.35       $1,043.1100   $1,043.10   $1,043.15   $1,043.00