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 $38.35   13.489%   $43.523   $43.52   $43.50   $43.50  
  Purchase #2 $212.25   3.480%   $219.6363   $219.64   $219.65   $219.60  
  Purchase #3 $59.31   8.455%   $64.3247   $64.32   $64.30   $64.30  
  Purchase #4 $248.44   4.813%   $260.3974   $260.40   $260.40   $260.40  
  Purchase #5 $179.79   12.415%   $202.1109   $202.11   $202.10   $202.10  
  Purchase #6 $175.44   8.436%   $190.2401   $190.24   $190.25   $190.20  
  Purchase #7 $21.45   9.180%   $23.4191   $23.42   $23.40   $23.40  
  7 purchase totals = $935.03       $1,003.6515   $1,003.65   $1,003.60   $1,003.50